Yeah, just a little every day, try to get the string around the stem, not the nug, it can cause damage, which can cause rot. But slow and steady man, you got the right idea. How do you have your intake fan set up? Or is that an out take? Do you have it blowing all the time, or only at certain times while the co2 is off? I bet if you play with it enough, and get a good source of fresh air from down low you can get your temps down below 80. It's fracking cold outside.
Dude, let me just say, even though it's your first grow, even though you threw your grow room together, you are pulling off a excellent first grow. I think with a little more room set up next round, and using less than 9 plants, and your going to blow that closet up with nugs. I think 9 is still a lot, but if you think you can rock it; rock it.
On another note: I've never used shooting powder at full strength, the idea has always scared me. Let me know how it goes.