triple leaf - even in brick??

hi, I am in the process of moving and will be building a studio in the garage of the new house, i will give exact spec once i move in but I have some general questions.. the lay out is something like below... the extension to the house would have been added on to a previous outside wall (meaning double layered) my concern is that if i add an inner plaster wall and "beef it up" that will be the 2nd layer then when i build the inner room it will be the 3rd leaf... is this an issue? the wall from the kitchen to garage (studio) will be brick - air space - brick - lots of platerboard air - new inner room.... any idea's? I know 3 layers is bad but is this even the case with Brick?? the sound going into the house is not such a problem but I will be using acoustic drums in the studio more than full bands so the bass may travel... ALSO the garage has a standard concrete floor, i am not yet sure if this will be better left as the studio floor or if I should build a false/floating floor? so: 1. any recomendations? 2. can a floating floor be added after the rest of the build is finnished if I then require it?? I have ben reading this forum for about 6 months but still get lost in many details... I am hoping to get builders to do most of my conversion so I know I need to get very clear pre build designs. thanks