damn, sounds like a nice setup man. co2 can be added anytime, and allows plants to grow in hotter environments. the whole yeast thing, i would avoid. levels are hard to control accurately and if you were able to afford all that other bomb equipment, might as well get the tank and regulator setup. on the other hand, if you have good venting, co2 isnt necessary. gives better (up to 2x) yields, but not necessary. best of luck man. i'm subscribed just cause of all your fancy shit! you get positive rep for being able to afford that.