Building a Golden Cuboid Listening Room garage

For along time I wanted to build such a room. Hopefully within a year or so I will. But first I am needing to know everything about materials and the best construction ideas before I procede.

This room will be outside of my home (garage type) and it will have room dimensions of 10ft(9ft) x 16ft x 26ft. I might even have the ceiling climbing from 9ft to 10ft to rear of room.(depending if this is beneficial or not)..

I am not overly concerned about sound getting out of the building , but more concerned of making it sound best inside:)

It will be on a concrete slab of 6 inches reinforced with steel (rebar). A 1 foot high knee wall will be built into the slab around the perimeter.

The walls will be 2x6 or 2x8.

Questions I have are:
1) Should I insulate under concrete slab with high density foam board. Any advantage for bass control ?

2) Should I build a subfloor over the concrete, or is it ok to just put down carpet etc..Any advantage for bass with or withought subfloor?

3) What type of wall insulation is best?, paneling gyprock?

4) Is it better to have thicker walls, 6 or 8 inch? what advantages?

5) Would it be better to have tapered walls and ceiling from front to back (smaller to bigger) or is the 10ft x 16ft x 26ft good enough.

Any other suggestions or ideas about building this would be appreciated. Hopefully some of you have a building like this with success.

I also have a number of DIY bass traps, acoustical foam and room lenses to help control some of the sound once it is built,if needed.

Thanks
Mike