Hey cool set-up....I like it. You know I found 400w of mh lighting a bit tough on my seedlings and having moved the 400 w into the growroom (where it ROCKS btw!.....just need to work out the electrical) and just bought a 250w mh w/internal ballast. I'll grab a pic in a few.

My seedlings honestly seem happier with a 250 and I can get it closer to them. Obviously it doesn't have as big a footprint as with a 400w so might be too small for your needs depending on how many seedlings you are going to be starting but I'm already seeing less heat and stress related issues with the 250w.

I'm not sure what to tell you about cooling Stealth.....when we had the 400w in a LARGE room the heat it left was minimal (approx 20 x25 ish)....but in the growroom(16 x 12 or something) I ended up hooking it to a 4" inline fan and DO notice a definite difference in the room cooling by perhaps 3-4 degrees with it running inline vs venting into room. I'm thinking that your new room will be smaller and may need some sort of good ventilation to assist.