I'd like some advice on what dimensions would be best for a grow cabinet.

Ok, here's what I'm working with, I've got 2x 150 watt hps lamps, a 4000 btu window air conditioner which I'm going to build into the cab (summer temps here get to be 95+ F, so no amount of airflow will solve my heat issues), and a tiny bathroom fan (~50 CFM) for ventillation (NOT for heat). I'd like to eventually do a SCROG grow since I think this will maximize my yield, but initially I'll be doing SOG so I can get females and clone 'em without having to disentangle all the males from a big screen. I could also supplement my lighting with some CFLs if necessary.

What do you think the dimesions (lengthxwidthxheight) I should be looking for are? Also if you have any advice on what pot size and how many plants I should be using (for my SOG or SCROG grows) that would be useful too. Thanks!