Put a tub sink in right next to the tank in the back of the garage. If it was mine, I wouldn't have ANYTHING open from the front - just a plain wall - come look at mine. Have them run dedicated circuits to the tank area, both GFCI and non-GFCI (for lighting - MH doesn't like them). You should also consider some type of air exchange system - you will be generating a LOT of heat, and you will have a very difficult time keeping that tank cool in the garage in the summer, even with a chiller. Might also consider insulated garage and doors, with central air.