Home studio in Sydney - need help with design please

Hi all, I have started building a studio underneath my house, next to the garage. When I bought the place there was already the majority of a room there, so I have it a little easier than starting from scratch. The room has 3 full walls and a retaining wall, which goes under the house (sloping upwards). I have since built a wooden frame/ top half to the retaining wall to completely enclose the room. See pictures below. The total room is about 16' x 13' (Sketchup shows metric - apologies to the Americans!). What I'm planning to do ... (a) A lot of the room is already double brick. Where it is only single brick I am going to add a layer of Rockwool insultation. (b) Where the retaining wall is, I have built a wooden frame above it to complete the wall. This will be filled with Rockwool insulation. I have then built a SECOND wooden frame (not quite touching) which will also be filled with rockwool insulation and then two layers of 13mm gyprock over that. (c) I then plan to build a room-within-a-room, using wooden stud walls filled with rockwool insulation and then with two layers of 13mm gyprock over the top. (d) The ceiling is currently just wooden beams with floorboards from the house above. I plan to pack rockwool insulation between the wooden beams, against the floorboards. THEN I will put a second layer of rockwool insulation between the Roof Gyprock and the first layer of insulation (there will be a small space between then). I was going to attach the ceiling gyprock using Resilient Channel (RC). Note - there is a steel beam through the middle fo the room that supports the house - not sure what the best way is to work with this?! (e) I was going to build a wooden stud wall where the window is, and put a second window in that wall. So it'll be window-space-window. Not sure if this will be quiet enough? (f) Not sure what to do with doors and/or Ventilation (rather important). My questions?! ... 1. Can anyone suggest a layout for the studio within the walls that I have shown here. I would ultimately like to have a Tracking Room for drums etc, a small Vocal Booth, and then the Control Room. Not sure if I have space. Otherwise I could leave the vocal booth. I have read with interest the many posts on this site and learnt a lot. I know I should have the control room certain dimensions. My roof is 2.2m high, or 7.2'. I will spend a lot of time in the Control Room so would like it to be as big as possible. 2. Is there anything else I can do with the ceiling to make it more soundproof? Unfortunately it's not very high and so I don't have much room to play with. 3. Suggestions on windows? 4. Do I need to do double doors? Or just good solid one's with rubber insulation around? I thought I'd do double glass sliding doors between the Control Room and the Tracking Room. Any comments or suggestions would be greatly appreciated. Great site everyone! Thanks John. I've learnt a heap here. Cheers Bruce

A quick update ... I have added the initial Rockwool insulation where these is only single brick. Still keen for any suggestions on the internal layout - from someone who has technical expertise in room design?! Cheers Bruce