I'd plan on getting something set up to move the air around more. That's a lot of space for a single unit mounted high and in one corner. You might run into "overheat" issues with the unit even though the temp on the floor is moderate. I have a buddy in the business and we were just talking about this problem a shop near Rathdrum (sounds like you're in the same climate zone) was having. They installed a fan blowing air from the floor up towards the back of the unit. Where is your thermostat in relation to the unit?
As for the walls....do it right now so you don't have to move all that shelving/equipment/etc to do it again in a few years. My $.02...not that I follow my own advice.