diff --git a/src/main.cpp b/src/main.cpp
index bf7a1d5..a292727 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -36,7 +36,7 @@ void activateSD()
 
   if (!SD.begin(CS_SDCARD))
   {
-    Serial.println("SD initialization failed!");
+    Serial.println(F("SD initialization failed!"));
   }
   SDActive = true;
 }
@@ -112,15 +112,23 @@ void handleUpload(AsyncWebServerRequest *request, String filename, size_t index,
     activateSD();
 
     // Check if file already exists and create backup name if needed
-    String filepath = "/" + filename;
+    String filepath;
+    filepath.reserve(1 + filename.length());
+    filepath = "/";
+    filepath += filename;
     if (SD.exists(filepath))
     {
       String baseName = filename.substring(0, filename.lastIndexOf('.'));
       String extension = filename.substring(filename.lastIndexOf('.'));
       int counter = 1;
+      filepath.reserve(1 + baseName.length() + 1 + 10 + extension.length());
       do
       {
-        filepath = "/" + baseName + "_" + String(counter) + extension;
+        filepath = "/";
+        filepath += baseName;
+        filepath += "_";
+        filepath += counter;
+        filepath += extension;
         counter++;
       } while (SD.exists(filepath) && counter < 100);
 
@@ -162,13 +170,13 @@ void handleUpload(AsyncWebServerRequest *request, String filename, size_t index,
       // ensure we close while holding the lock to keep SD state consistent
       request->_tempFile.close();
       sd_lock_release();
-      request->send(500, txt_plain, "Write error");
+      request->send_P(500, txt_plain, PSTR("Write error"));
       return;
     }
 
     // Flush data periodically to ensure it's written
-    if (index % 2048 == 0)
-    { // Flush every 2KB
+    if (index % buffer_size == 0)
+    { // Flush every so often
       request->_tempFile.flush();
     }
     sd_lock_release();
@@ -186,7 +194,7 @@ void handleUpload(AsyncWebServerRequest *request, String filename, size_t index,
 
       Serial.print(F("Upload Complete: "));
       Serial.print(filename);
-      Serial.print(", size: ");
+      Serial.print(F(", size: "));
       Serial.println(humanReadableSize(index + len));
 
       // Rebuild directory tree to include new file (guarded)
@@ -194,11 +202,11 @@ void handleUpload(AsyncWebServerRequest *request, String filename, size_t index,
       rootNode.buildDirectoryTree("/");
       sd_lock_release();
 
-      request->send(200, txt_plain, "Upload successful");
+      request->send_P(200, txt_plain, PSTR("Upload successful"));
     }
     else
     {
-      request->send(500, txt_plain, "Upload failed");
+      request->send_P(500, txt_plain, PSTR("Upload failed"));
     }
   }
 }
@@ -215,7 +223,7 @@ void handleMoveFile(AsyncWebServerRequest *request)
     sd_lock_acquire();
     SD.rename(from, to);
     sd_lock_release();
-    Serial.println("Moved file: " + from + " to " + to);
+    Serial.print(F("Moved file: ")); Serial.print(from); Serial.print(F(" to ")); Serial.println(to);
     // Rebuild directory tree to update file list (guarded)
     sd_lock_acquire();
     rootNode.buildDirectoryTree("/");
@@ -224,8 +232,8 @@ void handleMoveFile(AsyncWebServerRequest *request)
   }
   else
   {
-    Serial.println("File not found: " + from);
-    request->send(404, txt_plain, "File not found.");
+    Serial.print(F("File not found: ")); Serial.println(from);
+    request->send_P(404, txt_plain, PSTR("File not found."));
   }
 }
 
@@ -240,17 +248,17 @@ void handleDeleteFile(AsyncWebServerRequest *request)
     sd_lock_acquire();
     SD.remove(filename.c_str());
     sd_lock_release();
-    Serial.println("Deleted file: " + filename);
+    Serial.print(F("Deleted file: ")); Serial.println(filename);
     // Rebuild directory tree to update file list (guarded)
     sd_lock_acquire();
     rootNode.buildDirectoryTree("/");
     sd_lock_release();
-    request->send(200, txt_plain, "File deleted.");
+    request->send(200, txt_plain, F("File deleted."));
   }
   else
   {
-    Serial.println("File not found: " + filename);
-    request->send(404, txt_plain, "File not found.");
+    Serial.print(F("File not found: ")); Serial.println(filename);
+    request->send_P(404, txt_plain, PSTR("File not found."));
   }
 }
 
@@ -288,12 +296,12 @@ void playSongById(uint16_t id, uint32_t continueSeconds = 0)
   if (mp3File.length() == 0)
   {
     currentNode = nullptr;
-    Serial.print("Empty file path for ID: ");
+    Serial.print(F("Empty file path for ID: "));
     Serial.println(id);
     return;
   }
 
-  Serial.print("Playing by ID: ");
+  Serial.print(F("Playing by ID: "));
   Serial.println(id);
   Serial.println(mp3File);
 
@@ -314,7 +322,7 @@ void playSongById(uint16_t id, uint32_t continueSeconds = 0)
   }
 }
 
-void playSongByName(String song)
+void playSongByName(const String &song)
 {
   if (song.length() == 0)
   {
@@ -348,24 +356,24 @@ void playSongByName(String song)
     return;
   }
 
-  Serial.println("Playing song: " + mp3File);
+  Serial.print(F("Playing song: ")); Serial.println(mp3File);
   deactivateRFID();
   activateSD();
 
   if (!playFile(mp3File.c_str()))
   {
-    Serial.println("Failed to play file: " + mp3File);
+    Serial.print(F("Failed to play file: ")); Serial.println(mp3File);
     currentNode = nullptr;
     return;
   }
 }
 
-void playSongByPath(String path)
+void playSongByPath(const String &path)
 {
   playFile(path.c_str());
 }
 
-void playSongByRFID(String id)
+void playSongByRFID(const String &id)
 {
   if (id.length() == 0)
   {
@@ -463,7 +471,7 @@ void playSongByRFID(String id)
       folderFlatIndex = 0;
       DirectoryNode *startNode = folderFlatList[0].first;
       int fileIdx = folderFlatList[0].second;
-      Serial.print("Shuffle start: ");
+      Serial.print(F("Shuffle start: "));
       Serial.println(startNode->getMP3Files()[fileIdx]);
       startNode->setCurrentPlaying(startNode->getMP3Files()[fileIdx]);
       currentNode = startNode;
@@ -553,7 +561,7 @@ void playNextMp3()
     currentNode->setSecondsPlayed(0);
   }
 
-  Serial.print("Advancing to ");
+  Serial.print(F("Advancing to "));
   String mp3File = currentNode->getCurrentPlaying();
   // FIXME crash here if last song.
   if (mp3File.isEmpty())
@@ -598,12 +606,12 @@ void writeSongProgress(const char *filename, uint16_t id, uint32_t seconds)
     file.println(seconds);
     file.close();
 #ifdef DEBUG    
-    Serial.println("Progress written: ID " + String(id) + ", s " + String(seconds));
+    Serial.print(F("Progress written: ID ")); Serial.print(id); Serial.print(F(", s ")); Serial.println(seconds);
 #endif
   }
   else
   {
-    Serial.print("Error opening file for writing: ");
+    Serial.print(F("Error opening file for writing: "));
     Serial.println(filename);
   }
 }
@@ -614,7 +622,7 @@ boolean readSongProgress(const char *filename)
 
   if (!file)
   {
-    Serial.print("Error opening file for reading: ");
+    Serial.print(F("Error opening file for reading: "));
     Serial.println(filename);
     return false;
   }
@@ -660,13 +668,13 @@ boolean readSongProgress(const char *filename)
   // Validate ranges before assignment
   if (tempId < 0 || tempId > 65535)
   {
-    Serial.println("Invalid song in progress: " + String(tempId));
+    Serial.print(F("Invalid song in progress: ")); Serial.println(tempId);
     return false;
   }
 
   if (tempSeconds > 4294967295UL)
   {
-    Serial.println("Invalid seconds in progress: " + String(tempSeconds));
+    Serial.print(F("Invalid seconds in progress: ")); Serial.println(tempSeconds);
     return false;
   }
 
@@ -674,8 +682,8 @@ boolean readSongProgress(const char *filename)
   currentSongSeconds = (uint32_t)tempSeconds;
 
 #ifdef DEBUG  
-  Serial.println("Data read from file: " + data);
-  Serial.println("Parsed ID: " + String(currentSongId) + ", s: " + String(currentSongSeconds));
+  Serial.print(F("Data read from file: ")); Serial.println(data);
+  Serial.print(F("Parsed ID: ")); Serial.print(currentSongId); Serial.print(F(", s: ")); Serial.println(currentSongSeconds);
 #endif
 
   return true;
@@ -683,7 +691,7 @@ boolean readSongProgress(const char *filename)
 
 
 // Function to save the rfid_map to the mapping file
-void saveMappingToFile(const String filename)
+void saveMappingToFile(const String &filename)
 {
   File file = SD.open(filename, FILE_WRITE);
   if (file)
@@ -728,15 +736,15 @@ void editMapping(AsyncWebServerRequest *request)
 
     rfid_map[rfid] = MappingEntry(song, mode);
     saveMappingToFile(getSysDir(mapping_file));
-    request->send(200, txt_plain, "Mapping updated");
+    request->send_P(200, txt_plain, PSTR("Mapping updated"));
   }
   else
   {
-    request->send(400, txt_plain, "Invalid parameters");
+    request->send_P(400, txt_plain, PSTR("Invalid parameters"));
   }
 }
 
-void readDataFromFile(String filename)
+void readDataFromFile(const String &filename)
 {
 
   File file = SD.open(filename);
@@ -769,7 +777,7 @@ void readDataFromFile(String filename)
             mode = mstr.charAt(0);
         }
 #ifdef DEBUG
-        Serial.println("found rfid mapping for " + target + " mode " + String(mode));
+        Serial.print(F("found rfid mapping for ")); Serial.print(target); Serial.print(F(" mode ")); Serial.println(mode);
 #endif        
         // Add key-value pair to the map
         rfid_map[key] = MappingEntry(target, mode);
@@ -943,7 +951,7 @@ void stop()
 {
   if (audio.isRunning())
   {
-    Serial.println("stopping audio.");
+    Serial.println(F("stopping audio."));
     audio.stopSong();
     if (currentNode != NULL)
     {
@@ -1003,14 +1011,14 @@ void previous()
     return;
   }
 
-  Serial.print("previous(): Current song: ");
+  Serial.print(F("previous(): Current song: "));
   Serial.println(currentSong);
 
   // Use audio library's current time instead of tracked seconds for more accuracy
   uint32_t currentAudioTime = audio.getAudioCurrentTime();
-  Serial.print("previous(): Current audio time: ");
+  Serial.print(F("previous(): Current audio time: "));
   Serial.print(currentAudioTime);
-  Serial.println(" seconds");
+  Serial.println(F(" seconds"));
 
   // Try to go to previous within current directory first
   DirectoryNode *newNode = currentNode->goToPreviousMP3(2); // Use 2 second threshold
@@ -1023,14 +1031,14 @@ void previous()
     if (currentSong == newSong && currentAudioTime > 2)
     {
       // Restart current song if it's been playing for more than 2 seconds
-      Serial.println("previous(): Restarting current song");
+      Serial.println(F("previous(): Restarting current song"));
       audio.setAudioPlayPosition(0);
       currentNode->setSecondsPlayed(0);
     }
     else if (currentSong != newSong)
     {
       // Move to previous song in same directory
-      Serial.print("previous(): Moving to previous song in directory: ");
+      Serial.print(F("previous(): Moving to previous song in directory: "));
       Serial.println(newSong);
       currentNode = newNode;
       stop();
@@ -1079,7 +1087,7 @@ void previous()
 
 void audio_eof_mp3(const char *info)
 {
-  Serial.println("audio file ended.");
+  Serial.println(F("audio file ended."));
   if (prepareSleepMode)
     return;
 
@@ -1169,7 +1177,7 @@ void readRFID()
   stop();
   lastUid = newUid;
 
-  Serial.print("Card UID: ");
+  Serial.print(F("Card UID: "));
   Serial.println(lastUid);
 
   // rfid.PICC_DumpDetailsToSerial(&(rfid.uid));
@@ -1278,7 +1286,7 @@ void init_webserver() {
                 webreq_enter();
                 request->onDisconnect([](){ webreq_exit(); });
                 // Stream the response directly from the directory tree to avoid large temporary Strings
-                AsyncResponseStream* stream = request->beginResponseStream(txt_html_charset, 512);
+                AsyncResponseStream* stream = request->beginResponseStream(txt_html_charset, buffer_size);
 #ifdef DEBUG                
                 Serial.printf("Serving /directory heap=%u webreq_cnt=%u numOfFiles=%u\n", (unsigned)xPortGetFreeHeapSize(), (unsigned)webreq_cnt, rootNode.getNumOfFiles());
 #endif                
@@ -1294,7 +1302,7 @@ void init_webserver() {
                 webreq_enter();
                 request->onDisconnect([](){ webreq_exit();});
                 // Stream mapping to avoid building a large HTML String
-                AsyncResponseStream* stream = request->beginResponseStream(txt_html_charset, 512);
+                AsyncResponseStream* stream = request->beginResponseStream(txt_html_charset, buffer_size);
 #ifdef DEBUG                
                 Serial.printf("Serving /mapping heap=%u webreq_cnt=%u\n", (unsigned)xPortGetFreeHeapSize(), (unsigned)webreq_cnt);
 #endif                
@@ -1324,35 +1332,35 @@ void init_webserver() {
               {
         webreq_enter();
         request->onDisconnect([](){ webreq_exit(); });
-        request->send(200, txt_plain, "start"); 
+        request->send_P(200, txt_plain, PSTR("start")); 
         start(); });
 
     server.on("/toggleplaypause", HTTP_GET, [](AsyncWebServerRequest *request)
               {
         webreq_enter();
         request->onDisconnect([](){ webreq_exit(); });
-        request->send(200, txt_plain, "toggleplaypause"); 
+        request->send_P(200, txt_plain, PSTR("toggleplaypause")); 
         togglePlayPause(); });
 
     server.on("/stop", HTTP_GET, [](AsyncWebServerRequest *request)
               {
         webreq_enter();
         request->onDisconnect([](){ webreq_exit(); });
-        request->send(200, txt_plain, "stop"); 
+        request->send_P(200, txt_plain, PSTR("stop")); 
         stop(); });
 
     server.on("/next", HTTP_GET, [](AsyncWebServerRequest *request)
               {
                   webreq_enter();
                   request->onDisconnect([](){ webreq_exit(); });
-                  request->send(200, txt_plain, "next");
+                  request->send_P(200, txt_plain, PSTR("next"));
                   next(); });
 
     server.on("/previous", HTTP_GET, [](AsyncWebServerRequest *request)
               {
                   webreq_enter();
                   request->onDisconnect([](){ webreq_exit(); });
-                  request->send(200, txt_plain, "previous");
+                  request->send_P(200, txt_plain, PSTR("previous"));
                   previous(); });
 
     server.on("/playbyid", HTTP_GET, id_song_action);
@@ -1434,14 +1442,14 @@ void setup()
 
   if (continuePlaying)
   {
-    Serial.print("deleting ");
+    Serial.print(F("deleting "));
     Serial.println(progressPath);
     SD.remove(progressPath);
   }
 
   deactivateSD();
   activateRFID();
-  Serial.println("RFID");
+  Serial.println(F("RFID"));
 
   // Init MFRC522
   // Init SPI bus
@@ -1466,7 +1474,7 @@ void setup()
   // Optimize audio buffer size to save memory (ESP32-audioI2S optimization)
   audio.setBufferSize(8192); // Reduced from default large buffer (saves 40-600KB!)
 
-  Serial.println("Audio init");
+  Serial.println(F("Audio init"));
 
   lastVoltage = getBatteryVoltageMv();
 
@@ -1475,7 +1483,7 @@ void setup()
   AsyncWiFiManager wifiManager(&server, &dns);
 
   // Memory optimizations for WiFiManager
-  wifiManager.setDebugOutput(true);        // Disable debug strings
+  wifiManager.setDebugOutput(false);       // Disable debug strings
 
   // Reduce timeouts to free memory faster
   wifiManager.setTimeout(180);             // Reduced from 180
@@ -1493,7 +1501,7 @@ void setup()
   {
     init_webserver();
     server.begin();
-    Serial.println("Wifi init");
+    Serial.println(F("Wifi init"));
   }
   else
   {
@@ -1513,7 +1521,7 @@ void setup()
       0);         /* Core where the task should run */
 
   lastInteraction = millis();
-  Serial.println("Init done.");
+  Serial.println(F("Init done."));
 }
 
 void id_song_action(AsyncWebServerRequest *request)
@@ -1530,7 +1538,7 @@ void id_song_action(AsyncWebServerRequest *request)
     }
   }
   lastInteraction = millis();
-  request->send_P(200, txt_plain, "ok");
+  request->send_P(200, txt_plain, PSTR("ok"));
 }
 
 void progress_action(AsyncWebServerRequest *request)
@@ -1548,7 +1556,7 @@ void progress_action(AsyncWebServerRequest *request)
     }
   }
   lastInteraction = millis();
-  request->send_P(200, txt_plain, "ok");
+  request->send_P(200, txt_plain, PSTR("ok"));
 }
 
 void volume_action(AsyncWebServerRequest *request)
@@ -1566,7 +1574,7 @@ void volume_action(AsyncWebServerRequest *request)
     }
   }
   lastInteraction = millis();
-  request->send_P(200, txt_plain, "ok");
+  request->send_P(200, txt_plain, PSTR("ok"));
 }
 
 const String getSysDir(const String filename)
@@ -1760,9 +1768,9 @@ void loop()
     {
       if (voltage_threshold_counter > 3)
       {
-        Serial.print("deep sleep due to low volts (");
+        Serial.print(F("deep sleep due to low volts ("));
         Serial.print(lastVoltage);
-        Serial.print(") min: ");
+        Serial.print(F(") min: "));
         Serial.println(config.minVoltage);
 
         lastInteraction = millis() - config.sleepMessageDelay;
@@ -1833,7 +1841,7 @@ void loop2(void *parameter)
     }
     if (!loggingDone)
     {
-      Serial.println("loop2 started");
+      Serial.println(F("loop2 started"));
       loggingDone = true;
     }
     vTaskDelay(1);