1) See the Mobhack help, Units tab, Sound. You can override the default hard-coded sounds here on a per-weapon slot basis for each unit.
2) if you need new weapons sounds, you will need to create your own then place in /game data/sounds and assign the WAV files by editing Sounds.ini either to override a default or add a brand new sound (use one of the null slots for that).
3) you can override the battle sound defaults with your own background sound track files in sounds.ini as well. Up to 10 tracks to play sequentially, e.g. Glenn Miller for say WW2, if yu desire
!
Cheers
Andy