New studio/control room in basement, advice needed

Hello all, we are in the process of building our own place.....and i would like to setup the basement as a music studio. The basement consists of 2 rooms, a home theatre room and a 2nd room. The basement is completely underground and its four walls are made of steel reinforced 200mm concrete foundation, similar to that of a swimming pool. My aim is to make the 2nd room a control room which will double as a band rehearsal room. When recording i can use the home theatre as the studio room. As a result, sound isolation and making the control room as sound proof as possible is a must. The staircase down into the basement leads directly into the home theatre, and there will be a door from the home theatre to get into the control room. The wall which divides the home theatre and the control room is made of concrete (besa blocks) back filled with concrete. These bricks are also 200mm deep. See the floor plan of the basement below. At the moment there is no wall which separates the control room and the staircase, so a wall needs to be constructed which divides the control room from the staircase. Here i have 2 options: 1. Construct a wall from floor to ceiling which covers the entire staircase and have a door from the control room which will lead into the space under the staircase. This will allow this small room to be used as a vocal booth or storage space. 2. Construct a wall only above the staircase itself and leave the space under the staircase open and apart of the control room. I have basically decided on option 1 as i feel this will allow me to try and get as much sound isolation as possible. Although i am open to suggestions..... Now i have been doing a fair bit of research into ceiling and wall construction, which gyprock (plasterboard) and insulation to use etc, but really need some help to decide on what to use, how thick to make the walls etc. Basically for the 3 non staircase walls in the control room i am thinking of constructing a single stud wall with 1 layer of insulation and 1 or 2 layers of plasterboard. In total about 100mm on top of the concrete wall/foundation. However for the staircase wall, i am thinking of a double stud wall with plasterboard on eitherside. My concern is space, i really dont want to make this wall too thick, say more than 200mm. is this enough? I have also been looking into an air gap between the two studs....is this necessary? is there a minimum width this gap should be? At this stage I really need some advice/help with what to do with the construction of the walls and ceiling. I dont have a budget as such and am happy to spend a decent amount of cash to get the job done properly. Any help/advice/suggestions on the construction of my studio would be greatly appreciated......i can supply photos of the basement if necessary Cheers, Nick.