Where im at legaaly I can have 24 total. 12 veg 12 flower. Im gonna go to the store either monday or tuesday to figure out whats in my price range. not to sure on co2 systems but im gonna get a tank and a very slow regulator, theres timer and regulators that work together there around 100 dollars apiece , Im gonna get everything i need and post it in a journal so you'll see the benefits if any . With the exuast system Im thinking of the timer will put it on every hour or whatever , I could use a termastat also . Anyways probley need 2 400 watt mh's. I want to do 6 plants per light but I f im getting clones from someone probley could squeez more I guess.