1 flo light for veg should be good but you'll need a lot more light for flowering a mh or hps would be good. I think you"ll at lest a 400 watt if you doing 4 plants. I picked up a 400 watt hps for $100 on ebay.I use to use flo for both stages but the yeild sucks small buds. Now with my hps i get some nice big buds.
if you have the option definitely go w/ hps, but if you wanna stick to cfl's then i'd say get as many as you can stick in your cab w/o overheating it. as a general rule i try to stick to 3 42 watters per plant.