My rehearsal room at the top floor. Floating!

First of all I must apologize to all of you for my obvious inexperience in matters regarding constructions, anyway I'l do my best to communicate as best I can with a terminology so new to me. Here is a preplan for a rehearsal room at the top floor of an old building in Arona, small city by the Lake Maggiore in Italy (40 miles from Milan). The most interesting thing about this project is that even thought this is a second floor, I'm going to build the floating structure of this room on a 4" floating concrete slab. The idea that makes this possible (agreed by a local engineer) is centered on reducing the overall weigh of the structure by cutting down the existing 29 3/4" slab to 8 1/4". On top of the reduced slab I will lay two rockwool panels (2" each, 70 or 100 kg/mq³). On top of the rockwool will seat the fatidic 4" new concrete floor. The new walls will be built on the floating floor, and the ceiling (about the setting-up of which I haven't got a clear idea yet) will be lean on on the new walls. As you can see from the picture below, this is a small room (14 x 11,3 ft) built with very deep walls made of stone except for the one which separates the rehearsal room from the rest of my house. This thinner wall is a standard hollow brick structure rendered with mortar on both sides, which, as we know, is a bad client. Other various points of interest: - The existing window will be closed with sand bags, rockwool and gypsum - The existing door will be replaced by two acoustically efficent new doors - The air conditioning system will be realized with a Daikin system called "Ururu Sarara" which will take care of the recirculating process as well. - Neighbors are sort of everywere except upstairs, BUT, another building is just 8 feet away from my roof A couple of questions to which I haven't find an answer yet: What is the best strategy for dealing with my walls? Better to relay: a) on a classic two leaf structure all around the perimeter, possibly upgrading the hollow bricks wall with one or two gypsum layers and putting more air space? b) or to use the two leaf structure for all the walls except the weak one, which, since is going to configurate a 3 leaf structure anyway, could have two indipendent staggered frames in front of it, each of them supporting 3 layers of 5/8" gypsum boards on the respective outer faces? Which one of the two option would give the best isolation to a 3 element band who plays jazz and fusion? Obviously if none of the option is good I'm happy to get your suggestions. Ciao!