I am converting the rear half of a double garage into a multi purpose room with the main uses being a home gym and a full drum kit, so as much noise isolation as possible needed.

I have never done anything like this so input welcome! I have a circular saw, jigsaw, impact driver and combi and hand tools.

The front half has 2 metal garage doors and used for storage and bike access. The space I’ll have for the new room at the rear (access from side door) is 550x300.

The plan (AI rendition above)

External walls  
\- replace 1 brick on each existing wall with an air brick  
\- foil insulation on the existing wall pillars sticking out.

Floor  
\-creating a single brick high outline 50mm from the existing walls and for the new partition wall (creating a rectangle with well which I can use self leveling compound)  
\-laying a DPM within the rectangle going up the single brick and across the brick top.  
\- poring self leveling compound on the DPM  
\- laying 50mm PIR on the compound  
\- laying ply on the PIR  
\- laying 20mm gym flooring on the ply

Internal walls and ceiling  
\-stud framework built with 2’x4’  
\- sole plate attached to brick rectangle (through DPM)  
\- gaps in studs filled with rock wool insulation  
\-PIR fitted to studs on inside side.  
\-sound board (plasterboard) fitted to celotex

Questions  
\-Anything I should change / incorporate / be aware of?  
\- Is 50mm celotex enough all around floor walls and ceiling?  
\- I want to hang a punch bag so was going to attach 2 2x4 together and lay across new walls (not attach to ceiling)

\- Gym will start as a punch bag, bench, weights, rack (ideally smiths) and a rower.

Garage conversion for gym and drums