Drum room from scratch: plans are in

Okay so I know these are rather simplistic plans but I'm hoping this will be a rather simple build (hah!). So this "studio" is a part of an extension to the house that is about to get built. 7m by 4.25m, 3m ceiling (internal dimensions). The plan at the moment is two layers of 16mm firestop plasterboard on the inside, and a double stud wall on the wall adjoining the rest of the house. The other three walls will be brick veneer. This should be standard Australian construction, so that means concrete slab, timber studs, brick veneer exterior and truss roof system. Airtight construction tips will be followed (sealant, foam backer rod etc). At the moment the ceiling will just be the two layers of plasterboard as well. Not sure if I need resilient channel. Gold insulation fibreglass batts all around, probably, depending on what products my building contractor can source easily. HVAC will be settled by a split system inverter at one end, and probably some sort of ERV system for fresh air exchange. I'm trying to look into silencer boxes and things to isolate sound from that end at the moment, so any tips are welcome. There are no windows, floor will be a wood laminate and the doors will be a double door construction, solid core with some kind of seal around (researching into that too). Possibly beefing them up with MDF or something, but lead sheeting is a bit rare where I am and I hope I won't need that. Hoping to leave them undrilled and use a push handle and a door closer on each one, but for security's sake I might have to put a lock on the inner (or outer, whichever is better) door. Really what I'm after is enough sound isolation so I can play drums at a reasonable level up to a reasonable hour. I play at ~100dB, and a reasonable hour to me is maybe 10:30, 11pm. I'm not too sure what's going to be needed in terms of exact numbers here though, maybe 50dB loss? I'm actually not too concerned about flanking sound travelling to the rest of the house, but rather sound escaping to annoy the neighbours. The nearest house is only about 5 metres away from the wall on the far right. Also, every now and again the dog goes nuts, a car drives by on the side road (about 15m away) and a truck rumbles on the main road (about 150m away) so I'd like to stop that noise getting in to the studio as well in case I decide to do some recording. That's a little bit in the future though, but I am already looking into building some acoustic treatment in the form of bass traps and clouds (one for over the drumkit with some LED downlights) so my drumming sounds better. Hey, I'll take whatever help I can get :lol: Any tips/links on door seals and silencer boxes would be welcome. Any thoughts, feelings, criticisms or interests at all, please do let me know. I'm open for advice. I'll keep this thread updated and let you know when construction actually begins. Cheers Celereon PS I've just got told I have council approval for the current plan so as soon as the funds come through it looks like we can go ahead!

what is the 700mm gap between the studio wall and what looks like an outer wall?

Ah forgot to mention, that's a retaining wall. Not attached to the building at all (except maybe through the concrete slab, I'm not sure what the actual construction for it will be like yet because the retaining wall people haven't got back to me).