Hi all. Rescuing a barn for conversion to a music studio. I am in Nova Scotia, in an area that gets down to maybe -8c.and up to 32c. When the wind gets nasty, you can watch the vapour blast horizontally into the ancient cedar shingles. Interior framing has stayed rot free for 100 years.

Because of the high ceiling and exposed wood, the space possesses acoustical magic that studio designers spend fortunes to create. The conventional insulating techniques would ruin this advantage, as well as the rustic vibe of the space.

After reading on this site and others, I am leaning toward external insulation, leaving the interior alone. I like the idea of a drainage plane and water barrier under new board and batten. I am interested in hearing opinions on methodology and materials that will get me to a reasonable performance level in the wall system without endangering the wood.
I have already applied steel roofing ( had to be done  first thing due to a windstorm), so I’m thinking I’ll hire foamers to shoot 5” of closed cell up there in the rafter bays. The 1” pine sheathing has the gaps you would expect, and is covered with old cedar shingles.
Would it be a high crime to leave the shingles in place and work over them? Obviously stripping them and removing every nail will be time consuming.
Can I create an air and water barrier with rigid insulation, covered with strapping and/ or a capillary break product? Which insulation and how much?
The space will not have plumbing and will be heated by a heat pump, powered by solar.
Not trying to build Passivhaus here, but interested in using readily available materials in the most clever way!