My number one piece of advice to a closet grower:
Consider your exhaust and light as ONE UNIT. Purchase them TOGETHER, with your room dimensions and exhaust location in mind. If you can't stay below 55% RH and 85'F, you will have problems, and nothing else will matter. Air cooled hoods are a MUST unless (and even in some cases if) you are running strictly flourescents.
Good luck!