To determine how many plants you can run, you need to know how and what you are going to grow. Is this going to be a SOG (sea of green)? Or are you going to grow trees? Plant selection plays a part also, some strains won't SOG as well as others.

Here's a link to growroom setup that I found invaluable when I was going through the process.
http://boards.cannabis.com/indoor-gr...ml#post1634161

From my own experiences with this, in a basement, pay close attention to your ventilation. I wanted "extra" capacity so I wouldn't have to run my exhaust at full setting (noise levels). But, even though I tried to go twice the CFMs that I calculated, I didn't end up with extra. Damn CFMs get eaten up quickly with filters, ducting bends, long runs. My advice is, if you can afford it, buy the most and best ventilation that you can get. You won't regret it.

Good luck and keep us informed of your progress!