First draft of new mixing studio

Hello, I'm in the planning phase of renovating my house. I've asked my architect to include a small mixing studio in his design. He'd put my studio in the middle of the first floor so it will separate my home office from my girlfriend's. So it's a box in a box with it's ceiling not touching the main room's ceiling. The bedroom is one floor up. The purpose of the room is to mix tracks recorded somewhere else and experience (surround) sound in the most ideal circumstances. The main room's inner dimensions are 930cm/610cm/270cm with two supports measuring 60cm/40cm each sticking out more or less halfway the long sides. The maximum outer dimensions of the mixing room are 430cm/310cm/240cm, allowing an 80cm wide corridor at each side and 30cm of headroom. The outer brick walls of the main room are filled with windows, a door, desks and cupboards. The main room's floor and ceiling are concrete slabs. Question is: what is the most ideal form of the mixing room's inner walls and ceiling, allowing for traps, diffusion and absorbsion where necessary? I don't need windows. Just a door and an entry for HVAC. My budget is 15k euro for construction, airco and acoustic treatment. What will go in here? A Toft ATB 32, 4 small racks of outboard, 5+1 speakers, a LED TV, 2 LCD monitors, a sofa, myself and occasionally a friend/client or two. Eager to hear your ideas, Floris.

i would put the CR to one side or the other to leave more open space around it, or turn it to fully divide the space and make it a bit larger.