Shit, you have lots of light, so why not use 5-gallon pots and grow some big mamas? I used 2-gallon pots once, and the plants were relatively puny compared to the plants that grew out of 4-gallon pots -- half the size, maybe even a third the size. Large root mass = big plants = lotsa bud.

I'd try 12 big plants (4- or 5-gallon pots). If you're stuck on the smaller pots, then I'd try 18-ish and see how it goes, then adjust as necessary for next time.