stay with 12 gauge wire with the loads you plan on running. and try and stick to 240v too, as much as possible with lights, fans etc.
Don't worry about that - only if you were feeding it power with Aluminum wire instead of copper - causes corrosion if not used with proper adapter...
if you do it at the right time of day, running new wire in an apt is not that hard. From the sound of things you might look into surface mount...
first off, if you are feeding 12 gauge wire with 30 amps you have exceeded code already. need to upgrade to 10 gauge wire to feed the subpanel...
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