Well for any kind of growing I always use Professional Sunshine Grow Mix I think its called, works great for me for indoor and outdoor growing. As for the size of the pot..that depends how big you want the plants. Im guessing from your 2'x5'x5' grow room you intend to keep your plants short and bushy. I think you could fit 10 in there..but keep in mind the more plants you have the more expensive it will get if you want quality pot. I wouldnt recommend using a pot smaller than 2 gallons, you could get away with less but keeping the pot small isnt the only way to keep the plant small you can also top or train your plant. I've seen people tie strings onto major branches to hold them down to keep them from reaching the light in small grow areas.
Sorry to say, there is no simple or cheap way to grow really good pot. And a little research just doesn't cut it, not trying to put you off but the most important thing to do is read read read. Forums like this can be a great help but the best way to learn is just pick a grow method that suits you for your first grow, try it out, and if you like growing then invest a little more money in it.
Anyways if you have any more questions feel free to ask Im sure someone will help you, and good luck with growing!
