The dominant male is about 6" and the rest a bit smaller, say 3.5"-5.5". Right now I've got 9, but I'll probably get rid of an additional male or two since I've got at least 4 left still and a couple I'm not sure about. I haven't vented any, but at this point I'm only convinced that 3 are females.
The tank is ~72"x18"x18". The lighting is a single 4' 50/50 T12, which leaves the corners darker and IMO, makes the tank look longer/bigger because you don't see an abrupt ending.