1) The more the better but I think 2 will suffice.
2) HELL no. You need a portable A/C (discounthydro.com). Plus you're going to need CO2 in your room and if it's sealed you will not be getting CO2. So you're going to have to invest in a CO2 generator too. Fans don't reduce the temps and neither do charcoal filters (still needed in a grow though).
3) I'd suggest 22 dual output pumps with 2 airstones in each bucket (20 plants + a reservoir which needs to be aerated too)
4) 20 plants being on their own bubblers with no reservoir would be a very high matinence thing.
5) Depending on where you live I would be careful of the energy and heat output you produce so that you don't get caught.

Goodluck buddy and keep us posted. Also, welcome to the forums. <3
Da1KrayzieThug Reviewed by Da1KrayzieThug on . Recomendations Seriously Needed!!! This is my first attempt at growing so if anyone can give me some serious help (Zandor perhaps???) on anything to improve our growroom I would appreciate it. We are using an attached car port garage the measures 10 feet wide by 20 feet long, we have completely sealed the room off except for the door leading from the apartment to the garage. We will be applying 2mil think mylar to all the walls and 1mil mylar to the ceiling. We are hoping to run 20 plants all thourgh DWC hydroponics... I guess Rating: 5