shop insulation - Vic?

[rodger.]

Heat will be electric, and I will only heat a few hours per day. On saturdays, I may use for longer.

Like mentioned earlier, I am committed to doing this properly. If this means tearing out drywall, so be it. The hardest part is finding out what is "appropriate".

[Beerboss]

Air movement trumps vapor diffusion.  Dense packed cellulose reduces air movement which in turn reduces the amount of moisture laden vapor entering the wall.  It doesn’t sound like you have much of a moisture source to begin with so it shouldn’t be a big issue not having a vapor retarder.  If you are not cooling the space in summer you do not have to be concerned with the vapor drive to the inside so if you did have a vapor retarder that wouldn’t hurt either.

As for interstitial condensation, materials like cellulose are capillary active.  For condensation to occur you need that right temperature / moisture content and a condensing surface.  You don’t have the condensing surface with cellulose.  Put a board and a glass of water in the ice box.  Once cold pull them out and see which one sweats.  Wood is capillary active.

You mentioned you have stove veneer.  That is concern if there is no air space behind it.  Stove is a reservoir cladding meaning it holds water.  If you do cool the interior during the summer and the stone gets wet (rain, dew, and sprinkling) then warms up you develop a big vapor drive to the interior.  You do not want that drive stopped by a VR.