That's not really a 5V LED. Please provide a product link to what you call the 12V LEDs as well.
An LED's brightness is based on the current. So, decrease your series resistor to 270ohm for each LED to get just about the most brightness that they are rated for.
Do NOT use more than 5 LEDs with that board by itself. Adding more is cheap and easy-ish but you need to a MAX7219 if you want to use more than 5 LEDs.
Also, you are currently powering your MP3 player off of your board and that's not good. To address this we need to now how you plan on powering this after you are finished programming it. Do you plan on continuing to use the USB power?