Eight ounces off two plants is totally possible. I recommend you ScroG them though, so you don't have to worry as much about light penetration. Try three plants to start. If it gets really bushy in there, then you'll know the next time to either use two plants or veg for a shorter amount of time. Sometimes you just have to experiment to get a feel for what works best for you, and get the timing right and stuff. Worst case, with three plants, if gets too overcrowded, you can pull one out, but with two plants, if that's not enough, it'd be too late to do much about it, so I guess three makes sense for a trial run.

Looks like enough space to me too. What are your ventilation plans? 400-watt light will generate some heat, and you can't keep it bottled up in there. That was always the prob I had with closets: the woman didn't want me hacking or sawing on the walls or doors or anything, so that pretty much ruled out closets for me, except in emergency situations for a short period of time.