If sog is harvesting every two weeks , then they are only harvesting 1/4 of the plants. It takes 8/9 weeks to flower. The total harvested per flowering period is not based on number of plants. Just light and space. 2 oz per sq ft is a lofty goal. That is two pounds per 4x4 tray.
As a newbie start small. You are complaining that yoyr first planned grow wont be above 18 lbs? You are much more likely to not hit 10 if you went full bore on this. Shit with 10 x hps 1000w you are likely to screw something up first run.