My first grow/grow room.

Well I have recently decided to try growing my own marijuana, basically just because I need a hobby.
I live way out in the country, and we have an outdoor sauna building that we never use, figured I'd try growing in there. The space is, 7' wide, 6' feet from the floor to the ceiling, and 9' feet long. I have 10 feminized,autoflowering seeds, soil, pots, just the basics. I now need lights, a ventilation system, things like that, and had a few questions! I'm hoping there's some nice people around, so far I've just got hate from other websites which are bullshit..
Anyways, I was wondering if a 400w hps would work? Can I use a HPS light from seedling till its ready to harvest? Also, I live in southern Canada and it gets pretty cold this time of year, there is a heating option to the sauna though, it has a fireplace in the little entrance before going into the actual sauna, and that heats the inside of the building. would that be a good option, or would it like create humidity or some shit in the building? Inside, there is a small hole about 6 inches in diameter, and a chimney type deal that also leads outside, meant for the smoke from the fireplace. I'll upload pictures to give a better idea of what it all looks like. As far as ventilation, could someone give me a good idea of what i would need to ventilate the place, and keep the odor at a minimum.

You should post this in the Indoor forum, as it will get more views from peeps that have done this before. 400watts is nice, but not enough for the space or the number of plants, IMO. Of course, ventilation is a big deal, so you'll want to match lighting to the ventilation so temps stay in the zone. But if you can, look into more light. A 600w + your 400w. Or 2 600watters, or at least one more 400w light. The more light (properly directed) the more yield, so don't scrimp here. You can use HPS all season, or you can use MH for veg and HPS for flower, which will maximize yield. Unless it's super dry or humid, humidity may be the least important factor here. Humidity can be within a 40% range and be fine (30%-70%). In a room it's easy to add or remove humidity. Not so for temps. You'll want to keep those under 80, or so, if possible and not too cold at night. This can be hard to control You may also wish to consider using white panels/wallpaper on the walls to help reflect light.

Hope this helps, at least I bumped it to the top

Good luck!

R2T