Im making a grow box very similar to yours. For CFL's your going to need more then 1 for shure.

You need 2500 lumens per sqft of grow space.

I bought 6 23w 1600 lumen 2700k CFLs and im going to buy 6 23w 6500K CFLs today or tomorrow. To be honest I either need to get some more of these bulbs or buy bigger bulbs like 30w ones or something. You want to have plenty of lumens for your plants. I was going to use all 6 6500k bulbs for vegetative cycle and then switch to 6 2700k bulbs for flowering. My ideal goal is to have 3000 Lumens or more per sqft of grow space. Ile probably end up just buying 2 more 23w bulbs of both 2700k and 6500k grab 2 more light fixtures from home depot and have 8 of each for vegetative and flowering.

GL with your grow!