That sounds about right from what i've read. I just built a cabinet (still working on a few things left). Correction, i bought a Plastic Cabinet from store and installed the fans/lights/etc. I have 12 23 watter, 4 2700 and 6 6500 (or is it reverse, can't remember right now) for 260 total watts. It's smaller than your length wise, but around same height and width. I've seen people do PC grows w/ 100watts and get like an oz so i'm going for 2 oz min w 260w for first grow, i'd imagine you'd get the same.