As I mentioned the best approach is to decouple the walls and ceiling. Can be done with framing, clip&channel, or both.
For the floor you can either laminate more subfloor with damping compound, or add a massive rubber isolation mat to the floor and then double sheets of ply with damping compound. Dennis might have a comment on that, as he specs this in above grade room construction.
Plan the route of the sound controlled ventilation.
Plan for outlet seals, ceiling can lighting, and of course the doors.
Install insulation per local code. No foam, just standard fiberglass.
The Soundproofing Company