A little leak under the door won't hurt when running CO2. The biggest worry will be making sure your hood ventilation has no leaks.
For heat in the winter you have a couple different options.
Take your hood ventilation and draw from one corner of the room and vent to another.
If the heat is...
Depending on how much room you have and the temp swings something as simple as a few barrels of water can help regulate temps.
If possible I think a closed room is the best idea, using outdoor ventilation is too hot in the summer, cold in the winter, and risks contamination. That won't make the...
http://www.youtube.com/watch?v=6wXkI4t7nuc
I consider this lecture from a law professor and former defense attorney a must watch. Never talk to cops even if you're innocent.
You were legal four months ago. I would never let anyone know you're growing even though your legal, and especially don't let the cops or your city know it's begging to be harassed.
Sure looks like mites to me. Don't bother using a microscope looking for mites, as soon as you see spots like that just rip the leaf off and look at it with a HID behind it, if the mites are there you'll see them as darker spots.
If your pH is good you may need to feed them heavier to fuel the stretch. I had a similar problem starting out, I was only giving my plants 1 gallon of nutes in a 7 gallon pot, giving them two and upping the ppm slightly made everything better.
Starting out when people would say to me "How hard can it be to grow a weed?" I want to punch them. It's not hard to keep it alive, but to get the results you're looking for is a different story.