Hey,

The general rule for pot sizes is 1 gallon per foot of plant. I'd say once you take off the height you'll lose from your pots and the space from the light to the top of the plants you'll be left with about 4 ft, so 5 gallon pots doesn't seem that excessive to me. The one thing i'd point out is that you want to keep the plants in a square pattern rather than a straight line so the plants are getting an even distribution of the lights. Can you get two 5 gallon pots side by side in the 2.5 foot width of your closet? If not i'd get some a little smaller that will fit in that configuration.

I need to correct Keerons lighting advice tho. Sorry keeron, you said "put two cfl bulbs in and dats equal to you hps bulb" and "your electricity bill will be a lot cheaper" 400w hps and 400w cfl are only equal in the amount of electricity that they use (400 watts) so your electricity bill would be the same for the lighting. The lights are not equal in the amount of lumens they give out, hps produces far more lumens per watt than cfl and lumens is what the plants interested in, not watts.