Skip the plywood, go right ot the Comfortboard IS
I live in central Vermont, heating zone 6, hoping to get a little bit of feedback on the wall system I have in mind for a 4 season workshop (barn), with small efficiency apartment on the second floor.
From inside out: (1) Proper vapor retarding latex paint and primer, (2) air tight drywall system gaskets caulking and all, (3), freshly milled, green, 2×6 stud-wall, utilizing efficient framing techniques, and let-in bracing. (5) Cellulose or mineral wool batts in stud cavities (6) Comfortboard IS over stud-wall(7) Typar or Tyvek type WRB over Comfortboard IS (8) strapping (9) board and batten siding.
Also, considering using a variation of this in the roof system. swap (7) for an more appropriate roof WRB and (9) metal roofing, standing seam or Channel Drain.