tv/film mixing room

Hello,

I'm currently in the research phase of my mixing room build. The background is that I have access to a room to convert into a mixing room. This room was originally intended as a boardroom but is currently unused. It sits in the corner of a larger office space and was partioned with the help of 2 stud walls made from plasterboard. The other 2 walls are rendered brick walls and are the external walls of the building. The ceiling is not even and slopes upward from the back wall.The major problem I think is the amount of spill that the office gets. So i'm looking for ways to minimise it. I would also like advice about how to treat the front and back wall. All I've planned for at the moment is a primacoustics London kit for the walls, as well as a ceiling cloud. I have left the back wall empty as im not sure how to treat it. Is absorption required or diffusion? I will also add small acoustic tiles around the speakers on the front wall. I have a budget of around $2000 to apply changes to the existing structure.I'm planning on soffit mounting the speakers through the stud wall at the front. I can rest them on heavy duty speaker stands behind the wall.

Please help.

I didn't find the right solution from the Internet.

References:-
http://www.johnlsayers.com/phpBB2/viewtopic.php?f=1&t=19456
animated IT Security Video

Thanks