I have a similar shop building to yours, except ceiling is 12’ high-basically a two bay detached garage. In my case, no ceiling. Just open rafters and Sheetrock walls. I also have/had no insulation, and no heat. Well, there was a nice big heater hanging from the rafters when we bought the place. But the oh so erstwhile RE agent and honest seller forgot to mention it wasn’t hooked up - and that there was no incoming natural gas line leading to the building, or the heater! And the seller took it with him when he moved. So I lived with the shell for 15 years. No heat, just layers of sweaters and rugged he man winter work clothes.
Well, finally decided three years ago to tear out the sheet rock and put insulation in the walls. Each year I do 1/3rd of the shop. New insulation. New Sheetrock. And importantly, new wiring with an upgraded panel, upgraded single phase and three phase circuits. Everywhere. Now, This spring, I have only one wall to go. Then maybe I will tackle the ceiling. Or hire some guys to do the heavy lifting for me.
Moral of the story is it worked out for me to do the upgrades in smaller phases. It’s easier and more managble to hang rock, pull wire, tape-mid-paint, etc, if the extent of the work is broken down into small chunks. Cost gets spread out over several years also. Might be something to consider. As they say - how old will you be in three years, if you DONT upgrade?
Glenn