Eh, keep it one big chamber for now and do a few grows of mongo plants, the kind few indoor people can grow at all. If that should ever get boring (can't see why it would), or production quantity becomes more important than quality and simplicity, then break it in two. The fewer compartments, the simpler the ventilation system too, which probably translates into less upfront expense.

And with the one big compartment, with so much height, I'd consider putting like 12 3-bulb bathroom fixtures in there (3 on the left, 3 on the right, and 2 columns of 3 each on the back wall). Then you could put some El Cheapo 26 watt CFLs in those, for an extra 936 watts of sidelighting. If you used 42 watt CFLs, that'd be an extra (*cough*) 1512 watts of sidelighting. And it wouldn't be like you'd have to use them all all the time - just unscrew bulbs until you have as much sidelighting as you want. Or, if you put each fixture on a switch, you could just click them on from the bottom up as the plant(s) grow. Home Depot has the fixtures for about 10 bucks each (just bought a few myself, for the same use). Of course, they do generate more heat, so you'd have to build your ventilation system with that in mind, but I think a 6" inline centrifugal would handle it fine if you kept a small circulation fan in each back corner to move air around and used a cooltube on your primary light(s).