Dam you opened a monster right here. I wont get into the whole case of frequency balance and acoustic isolation. But usually your best bet is foam. I mean the only thing to stop sound and air is mass. For microphones in your home recording studio windscreens are a must. Always place far away from computer to keep away from hissing. I usually turn my ac on for about 10 minutes then just it off and start recording in case that happens again. I also block the bottom of the door from air. Doors are prob the biggest problem in recording studios. If you have ever seen one or been in a really good one you will notice you go through prob 2 or more doors till you actually get to the isolation room.

for listening back if you have nice speakers to playback your mix its very helpful if you have absorbtion and diffusion in your room. you always need something reflecting off the back of the walls and come back to the front of te room (where you are) and be absorbed by some kind of material. For frequency balance. When you record and your voice seems very bassy, if you ever record in your room. It prob means you need to cover up your corners. Bass loves corners and usually needs a very thick material. As I said again mass stops sound. The more seperate you isolate yourself from the outside world the better off you will be. The biggest problem with my studio is that I am in a second story house and I sometimes hear things fairly easy through the floor. So I bought a nice plateua to go right in my room with the microphone on top of it with rubber stoppers built into it to stop the sound.

Hope this helps. Its extremly hard (I know) to get a good acoustic isolated room with the construction already done.

but I tried to give you the tips to block out sound without the construction part.