I would plan for heating. A large building in Indiana will take a long time to heat up using portable heaters.

You could look into a mini-duct a/c-heater unit. We added two to our upstairs before we remodeled and added central air. It's easy to turn off when you aren't using it, and have it set to a thermostat when you are. They're more efficient than space heaters, so it might be even more environmentally friendly.

I wasn’t saying you should heat it all the time. It is much easier/quicker/cheaper to heat up a building with a furnace/heater than an electric space heater.

We have an accessory unit that my husband uses as his office/3D printing studio/painting studio. For several years, we just used portable space heaters, portable a/c, ceiling fans. Then we added a mini split. We obviously do not heat and cool it all of the time because that would be expensive and terrible. However, the mini split has made it so much easier to enjoy the space. Honestly, I think it may even be a little less expensive because it is more efficient.

For cooling much of the year install a variable speed whole house fan (5,000 - maybe 8,000 CFM?) in a high point in the building. Think about airflows from windows to the fan. Open some windows, turn on the fan and you've a very nice cool breeze and better yet - fresh air. Reality though is that some days may be too hot/humid for that to work to your satisfaction so then AC is needed. I've a 7,000 cfm WHF and a 3 head mini-split system. Most days the WHF does the job.

Electric heat is expensive unless you've a large enough solar array to cover all of your electrical needs plus the heating. In slab radiant with an efficient gas boiler works well though it takes time to heat up so you kind of have to pre-plan.