Good questions... trial and error is the best way to find out. As for the size of the room, well, as big as you can make it. Build it yourself or buy a used closet with flat white walls like mine. Here's a good link about grow room setup:

http://boards.cannabis.com/indoor-gr...-progress.html

I don't have any experience with small MH's... sorry. It's all about lumens, so the more lumens per square foot, the bigger the plants and the buds will be. I would aim for 5000 Lumens per square foot, or more. Also having the correct color (Kelvin #) for veg and flowering will make a difference. Since you have them already, try them out. But if the temps get high, get more cfl's instead. A couple more good links to answer your questions better:

http://boards.cannabis.com/indoor-li...-lighting.html

http://boards.cannabis.com/indoor-li...uch-light.html