Small studio for mixing and recording (one room design)

Hi everybody My name's Chris and I'm from Switzerland. This is my first post, so I hope I've done everything correctly. I'm a audio engineer and I purchased a house where I plan to build a small recording studio/control room in the cellar. The existing room dimensions are 4.7 m - 2.8 m - 2.1 m (length, width, height), the outer walls are concrete (30 cm thick), the inner walls brick (12 cm thick). There's a window 2.2 m x 0.5 m (see picture below). I want to start the construction in April 09. Mostly, I do on location recording so I want the studio to use for mixing (post production) and voice recording. I'm also playing the sax, the clarinet and the drums and want to exercise in the new studio room. The monitoring level would be 90 dBA, wood wind instruments and the drum kit produces up to 120 dBA. The neighbors are about 50 meters away. If so, sound isolation would be needed for the flat above the studio. But the room height is only 2.1 m! I've posted a first draft of a floor plan and a side elevation. A first layer of insulation with plasterboard is intended for heat insulation. There's a rear wall absorber (wide band) with acoustic hangers. The side wall absorber system is built with panel absorbers (lower half) and slat absorber (upper half). On each side of the mixing desk, there is a helmholtz resonator angled 10°. The front wall is a panel absorber for low frequencies. The goal is to reach a reverberation time less than 0.2 seconds over the hole frequency range (see reverberation time sheet below). For cooling and heating (HVAC) I planned to buy a inverter split system from de longhi with a noise level below 30 dBA for the indoor unit. All other systems (Computer, Server, Tape Machine etc.) are placed outside the studio. For monitoring I have Dynaudio BM6a and a BM14s subwoofer and I plan to use them as freestanding speaker as recommended by Dynaudio (heat problems, duct at the rear etc.). In a first step a stereo setup will do the job. Later I want to expand to a surround setup. Here are my questions - What do you think about my draft? - Do I need sound isolation? How is this achieved in such a small room? - What do you think about the amount of the different absorbers (right, too much)? - Are there other things worth to consider or what I should forget for such a small room? - Is there an easier design to reach the same goals? For me, this studio is an investment for the next 7 to 10 years. I'm willing to spend a few thousands swiss francs (US $ 2k – 4k). Any comments, suggestions are appreciated. Thanks a lot. Cheers, Chris