Sounds like a great plan with a lot of potential. I'm just worried that the open floor in the grow with just screening will leave you with a cleanliness problem, maybe fungus, bugs, and unwanted plants growing up in the dirt under the screen. If the room is eventually going to expand down a bit more, maybe you should remove all the dirt now through the AC window while it's all open; then make a floor something you can keep clean. Let me know if i'm not understanding you correctly, i'm a bit stoned.