1. Use 12 gauge Romex:
a. Anything heavier is too hard to work with.
b. 12 gauge wiring supports 20 amp wall receptacles.
c. 14 gauge (supports 15 amp receptacles) would work, but way not splurge?
d. BTW don't bother buying heavier gauge power cords than the wiring in the wall
2. User plastic electrical boxes
3. Ask him about running a separate ground for the audio system. Some swear at the idea, but that's what I've got and it works great. I've got a dedicated man room (audio/office) in a new build with it's own underground service/transformer, all new appliances, in the country with no industry nearby, and the above wiring scheme plus hospital grade cryo'd Hubbell receptacles.