To the levelup sound: the problem would be, that the sound would be heard not only for the one mech that leveled up, but for all in the near of the mech. Dont know how that would confuse the players, but i can test it.
I also had the idea of ig music, but because of the same problem, i m not able to bring it in (you would hear for each bot the same music parallel).
To the plasma weapons of the hvy: The heavy is still the most used and strongest mech, increasing his weaponpower would make him even stronger. Also i dont see a problem by trying to go into close combat - this makes the game faster and i think thats a good point.
To the assmissiles: yes, i can increase their turnrate. Have to test if an increasement of their impulse is good.
Edit:
lol i just checked the sound.. you dont want me to put this sound ig!!!I demand level up sounds now that you got walking sounds.
SMB powerup/1up