You can use as many, or few, CFL bulbs as you want. What it depends on is how large the plants get.
Personally, I suggest you keep your plants short and topped, beginning flowering sometime around day 25 to 30 from seed. The topping will help keep the canopy stay a little more even which is important with CFL bulbs. Incorporating some small grow through plant supports might help also.
Ideally, you're not going to spend more than $80 on the entire set up because at that point you may as well get a 150w HPS for more light with less energy at the same cost. Figure each bulb and socket is going to run you about $8 on the average. Figure a $40 setup would be 5 bulbs total. I wouldn't go over 7 bulbs, with three bulbs for each plant and a single bulb between them.
Clamp light reflectors are definitely the easiest and most efficient fixture's I've found. Get the medium sized ones (6" I think).
Some people drop the ol' watts per plant thing with CFL bulbs. Not entirely accurate. The key is to get the bulbs close to the plants and to minimize the loss of energy. Figure one bulb for every 3-4 inches of growth.
Flowering indoors happens when there is more dark than light. You need the tent ventilated and light tight.
Most people use 2700K CFL bulbs despite the light they produce being mostly unusable to the plant. I prefer mostly Daylight CFL bulbs from start to finish but it is good to incorporate some Soft White lighting.
A good setup would include three 27w Daylight bulbs per plant and a single 46w Soft White bulb between them using the circular design to maximum effect.
