Good point on understanding local rules about living spaces. It's rural Indiana zoned agricultural/residential so hopefully not a problem. Even if there's no living space I'll want sewer and water for a laundry tub so I'm not going back to the house all filthy. Where do you start to gather information on local requirements? The zoning commission? Some other county office? I don't want to count on a builder knowing the rules.
This is all handled by your local township (unless they defer to the county for permits and inspections).
Stop into the local township office and be friendly with everyone and ask to talk to the local building/zoning official, they can invite you in for a meeting to answer all your questions.
Thats the first thing I did when I bought my parcel of land, zoned residential-3, and was a bit dismayed to find I was not allowed to build a barn BEFORE having a primary dwelling (house) on site. The permits could be combined, and the barn could go first, but could not be separate process/permits. SO I had to work on my vehicles on gravel for a couple years before I could swing a pole barn. There were also many other restrictions and rules to follow that I was not aware of.
The other thing to do is find your local township website and download/read ALL of the zoning regulations. Specifically on buildings and land use, there will be a lot of information to absorb there.
In my case, at least 100' separation was required between well and septic field, didn't matter what was in between them (my house is, to shorten the plumbing in each direction).
Regarding interior finishing - you won't have "studs" with a pole barn unless you specifically frame in an entire wall in between each post, which kind of defeats the purpose of the pole barn and adds some significant cost. Many people do this anyway, but why not just stick-frame the whole building at that point.
Heat/AC - Yeah putting pex tubing in the floor when you pour the slab is cheap to add if you do the labor yourself of setting it up, and then you have by FAR the best heating method. You can just run an electric boiler or water heater if you want to keep it simple. I would personally not want a diesel-fueled heater in my shop requiring tanks, lines, exhaust, fire safety, etc. Propane is easier though.
If you keep the main floor at a reasonably comfortable temp all winter, then the upstairs can be run with a single heat-pump mini-split unit for both winter heat and summer A/C. Running A/C in the main shop is a tough call, its very nice, of course, but also very expensive. I don't have my heat and A/C done in my 30x36 pole barn yet, but I do plan to add a mini-split in the shop floor - not to hold the entire air space at 70°, but rather to blow cold air in at least one area for temporary relief as needed.
