Under a 400 watt HPS you can only have I think it was 6 ...that is if they are in a 5 gallon bucket. I ony have 5 under my 400 watt HPS but it feels like its still short on light. A 1k light you can put about 9 under there comfortably (5 gallon buckets that is). I think it all depends on how high you are planning on growing them. I would assume you could have more under one light the shorter your plants are.
As for the AC you have to be careful which one you choose. Its almost impossible to run a sealed room with a window or portable AC. The CO2 will go out with the hot air. They both have "exhaust" that will remove hot air from the room. Would be kinda hard to seal a room if you were running one of those. I havent used either of these ACs in my room so I cant help ya there. Maybe some fellow RIUers have exped with some of these and can post the pros and cons of such units.
Happy Growing!