i would go with 2 x 400watter, otherwise you will be constantly batteling the temps, plus you could put the extra cash to buying top of the range bulbs/ballast/reflectors rather than budget items....if you can stretch to it, cooltubes or cooled hoods are the way forward.

you could grow 8 plants, 10 at a push. you should be looking at least 12 ounces per crop, and that a low estimate.
just dont get greedy and buy the third light, spend it on 2 better lights and better ventilation.