Mewtwo Strikes Back
Converting a .wav file to a MIDI is hard enough. Converting a MP3 file is ever harder. Avoid such conversions anyway, as they're not worth the effort. You will experience enough problem to make your .mid file play the right way in the game. Just get the MIDI version of the song.
It's kinda crucial that you learn to find things yourself, sometimes. The table offset for FireRed US v1.0 is 0x48C914.