your limiting factors would be heat and space. as long as it doesn't get too hot (like over 85) and you've got the room then you can add more. i've only used CFLs for veg, but i don't think i would try flowering with less than 6 lamps assuming they are the ~26 watters (100 watt equivalent). like chimera said, the more the better. with CFLs and a fan blowing on the plants, you should be able to get the lights within a couple or three inches of the plants with no problems.
My first grow, I had 500+ watts of CFLs on ONE plant. As many as you can fit and keep the temps down.
see the problem with answering your question is that its not how many cfl's you can get, its how much wattage you can get on your plant. cfl's don't put out much in wattage so you want to find as many cfl's with the highest wattage possible. the more wattage you can get on your plant the bigger the buds
but dont get anything other than mv, hps, mh, cfl, or flouro. and cap-n-krunch how the hell did you have 500W. or was it 500W equiv?