Okay...
How to separate your Live room from your mix room:
You'll be framing one wall. Build it out of 2x6's (or metric equivalent). I know it's not a load-baring wall, but you'll still want to do it at 16-inches on center (That's a stud every 16 inches).
Once the wood frame is up, find ALL your gaps between your new wall and the existing room (there WILL be some). Fill them all with either "Spray-Foam" insulation, or Painter's Caulk. It doesn't hurt to Caulk the rest of the edges as well, all the way around the wall, wherever it meets with the existing room.
Then, run your electric work. I would go with, at least, 4 outlets and any necessary switches on EACH side of the wall.
Then, you'll want to pick a side to hang your first layer of rock. Use 2 layers of Drywall/Sheetrock. And YES, you want to put a "finish coat" of mud on the first layer before moving on to the second layer.
Once you have one side of the wall "rocked", insulate the wall. Stuff that bitch good too! You want so much insulation in there, that you'll doing some pushing to hang your next layer of rock over it. After insulation, put up 2 more layers of rock on the open side, not forgetting to mud/finish-coat each layer individually.
Then, install your door frame and door (make sure it's a solid-core door). Once the door frame is leveled and secured, you can drill some holes down the center and fill the air space with spray-foam insulation. Then hang the door, and caulk the frame to the wall.
Follow the same procedure with your window, if you are putting one in. But, make sure you know what you need to get the window done correctly. 2 sheets of double-pane glass, one needs to be about 1 inch wider than the other. You'll need to have already framed out for you window size. Whatever the measurements are for the smaller piece of glass, add a 1/4-inch to the height and width of the window frame, to give yourself some play. And remember: The smaller the window area, the smaller the chance for sound getting through.
The glass on the control room side can be mounted straight up and down, and therefor will be the smaller piece. But the glass on the live room side should be mounted at an angle, leaning out at the the top, which is why you'll need the wider piece. You'll need some trim wood. I usually use simple 1x1 square trim. Measure to the center of the window frame and nail a "spine" of 1x1 all the way around the inside-center of the frame. That gives you a "backer" to put your first piece of glass against. Once your control room glass is in place, secure the outside with trim wood the same way. And make sure it pushes the glass tightly against the trim "backer". You don't want that glass rattling around. Caulk all the trim on both sides to the glass and to the frame.
Then, in the live room, place the bottom edge of your 2nd piece of glass against the 1x1, so you'll wind up with at least 1 inch of air space between the 2 pieces of glass, at the bottom. Lean the glass up, into the frame, until it touches the frame at the top. Remember: This piece will be leaning out towards you at the top. Take a pencil or thin marker and draw a line, tracing the window, on the frame, while someone else holds the glass up. Then take your glass down for a minute, and nail trim "backer" along the inside of your lines, up the sides and along the top. This supplies you with your "backer" for the live room glass. Once again, put the glass in place and nail the trim wood in front of it so that it's tight, no movement in the glass. And once again, caulk all the joints.
Last, but not least... PAINT THE FUCKER! You'd be surprised how much sound will get through without a couple of coats of paint.
**If anyone has anything to add, besides the obvious "Don't forget to put up your studio foam", I welcome the input.
