Hey cyberaktif, congrats on the great grow and the awesome set up! I also built my own room in an outdoor building that is 10 x12. Inside I only have one grow room, 6x12, the rest is kind of like a boiler room where my timers, ballasts, reservoir , etc. I'm about 4 weeks out from harvest, hoping it goes well. My post is under first grow, first forum.
i can't help with your last question as I'm gaining experience and knowledge everyday.
But, I've read your awesome post and wanted to add my 2 cents on controlling room temp. I have been able to control heat/humidity quite well, even during the winter when it's been snowing one day, raining the next! Living in eastern Canada so winter is a mixed bag! The quick and dirty was that I used two low powered inline fans placed in my boiler room to either push air from the boiler over my HPS lights and vented outside. If it was really cold out, I could easily switch the fans to pull cold fresh air from outside over the lights, heating the air slightly inside the boiler room then it was pulled into the grow room with an adjustable 400cfm fan and then the grow room was vented with another adjustable 400 cfm fan to keep fresh warm or cool air moving in the room. Most times I had one fan pulling fresh air in over one light, and the other was pushing air out over the light. This ment that the only time I needed a heater was at night when I would turn the air exchange almost off so that my space heater in the grow could keep thing warm. Sorry for the long ramble. If your interested, I can post some pics, I heard somewhere there worth a thousand words.
the lights I'm referring too are two 600w HPS lights.