I second Zapped's advice, and add:
Do NOT ever use multiwire circuits!! They have, in my experience, caused more problems than they should.
The worst case I've run into so far was in a multi-million dollar mansion, with three-phase service, five circuits to the audio rack served with 5 #12's and ONE #10 neutral. And the client was wondering why he kept burning up power amps and had massive hum problems...
