1st off, a 23w CFL bulb with put off 1600-1700 lumens. A lumen is the total amount of visible light emitted from a source. For good results try to get 12,000-15,000 total lumens and that is cutting it close. Roughly, 10-12 23w CFL bulbs should suffice, but then your going to have temperature issues, unless your ventilation is superb. My 4x2 1/2x5 veg box reaches upper 70's with 10 bulbs, into 80's with all 12. Thats with a 4 inch exhaust, 4 inch, force air intake, inlet fan AND a 4 inch stir fan. I'd try for more than less light.

Just know that your going to lose 5% of your lumens per bulb if they are vertical. Meaning they will emit more light if they are sideways. Interesting fact that I just discovered.