NOT a double post guys, if someone can delete my previous one, please do, this is the edited version.

MY OPINION, I am not the pot pope, I can be wrong.

Well, i would suggest getting a switchable ballast, one that can run HPS AND MH bulbs.. a lot cheaper and easier. I'd suggest going with another 400W because you want between 30-50 watts per square foot when dealing with those HID lights; 16X30=480Watts (minimum) 16X50=800Watts (ideal, anymore and you start wasting light). So, just get another 400W, hang them apart so they cover the space evenly. If you can't afford switchables, stay with HPS, it may not be as good as MH in veg, but if grown strictly with either one, HPS gives you a substantially larger yield.

I'd strongly support using soil, unless you live 3+ stories and you have no elevator. Done correctly, organics can produce just as much bud (and much tastier mind you) in the same time as hydro, ok maybe at MOST a few days behind, but if you're looking for quality, stick with dirt.

Optimum number of plants would really depend on how you want to grow, I'd say anywhere between 8 and 16, leaning more towards 8, although, if you want quick turnaround and you don't mind making a lot of clones, go with 16. That way, you just veg for about a week, rather than 2 and put them into flower.

CO2 is a definite yes, especially as babies and when they're blooming, and if you're going to be doing quick SOG, that'd be perfect, as they go into bloom as babies.

My main problem with hydro is that it's messy, too much equipment to buy and maintain, very little cushion for mistakes, and you need to check it daily. Right now, I've got a grow going in a buddy's house, all he has to do is water it and feed it according to the directions. Nothing complicated, if he forgets to water for a couple days, nothing is going to happen. If the water levels get too low in hydro.. you're fucked, soil holds moisture MUCH better than air.

Your mother plant would be the one to use the SCROG technique on, so that you can use the available light efficiently. I'd go with 2-3 good cfl bulbs per square foot for her, cool white of course.

Oh, as far as cloning, check out my thread (I think you may have already.. dunno) search for "DIY bubbler cloner" the roots are going insane, and that's what you're looking for right? I'd go for a bubbler cloner rather than the rockwool method, for several reasons, one being that when you transplant, the rockwool will get kinda funky and attract unwanted pests/ fungus or bacteria.

I know you like doing the Scrog, but that's really designed more for people that only want a few large plants, it doesn't yield as much, takes a lot longer in veg, and honestly is a big headache. Just grow all the clones uniformly, quickly, and then you'll be able to use your floor space much more efficiently. Oh, and you'll have bigger buds because each bud will be a cola or slightly smaller rather than a bunch of little vienna sausage buds from a SCROG grow.

as for yield predictions, check out YOR - Advanced Yield Calculator I put your data in and got 1.16 pounds in soil and 1.38 pounds in hydro.

I'd say personally you could get at LEAST twice that. I know I can get up to 4 ounces per square foot.