First-time Attic Stealth Cabinet Grow

Hey everybody, first of all, let me just say that rollitup.org is awesome, and since I've started to be interested in growing it's been a super-valuable resource. The reason that rollitup.org is a good resource, though, is the people who get on rollitup. So I submit to you my plans for a low-budget stealth cabinet grow in my attic, so that your experience might better my grow.

Okay, first things first. I just bought some NLxWW seeds (crystal from nirvana), 5 ferminized, and a germ kit. The closet that I'm going to use is going to be 75-3/8”H x 19-5/8”D x 31-1/8”W, which is close to 6'x1.5'x2.5' for a total of 23 square feet.

Now, here come the questions for the community.
1) I'm planning on 400w HPS, at least, but is it worth the extra cash for me to get MH for veg? Is the faster and more aggressive veg growth worth the cost in terms of production?

2) My attic is warmish. For a cabinet grow with a 400w-er, am I going to have heat problems? I am going to have airflow from the outside using fans and such, but I'm worried. What else should I do to make sure my plants are at the right temperature?

3) The most obvious question: how many plants can I fit? I thought about doing a ScrOG grow, but 1 plant / square foot would mean I would need 23 plants which seems like a lot. For an indica/sativa cross like Crystal, I think I'll have enough room for the five plants?

Any other advice you could offer me would be great... I'm just a n00b trying to make my way. Thanks guys!

What's good, everyone.

Just decided to update you all on what's going on. I've gone ahead with decisions. 400w HPS + cooltube + timer, 4 4" inline fans and 25 feet of 4" ducting, grow tent [, BMO nutes, 5 ferminized crystal (NL x WW) seeds from Nirvana (not here yet) + germ kit. haven't gotten pots or soil yet. Whole setup has cost roughly 550, going the cheapest route possible.

SO obviously it's no longer a cabinet grow, and I'm not going to have it be a ScrOG grow either. I know how in my last post I confused square feet and cubic feet. I figured it out on my own. I was pretty baked last time around on some Korean crazy leg? No excuses.

I have many remaining questions, but I'll figure them out. At least give me your blessing, internet community.

Pics will be uploaded on this grow, but only sporadically. I hope my attic works for this shit. Later people.