That you are asking for opinions is a good move. On the otherhand, opinions are like ********, everyone has one and most of them smell pretty bad. I am facing a similar situation where I bouht the adjoining house to use as a shop. Good intentions usually go south when the unforseen comes to town. In my case, the last stroke putting me in a wheelchair.
You have a very nice barn, I would give my left foot for a place like that. I would say to build onto the front, 3 walls, to house motor vehicles, cars, bikes, tractor, et al. Then insulate the Hell out of the barn to use as a shop. Building stud walls, 4 inch furring, inside a block wall is no big deal. Same for the ceiling. And as already noted, insulating the upper level as well. The wide doors reused for the front and filled in to a 4 foot or so wide vestibule into the shop.
Because of the chair, I am (loosely) considering an attached garage. A basement is not off the list but is way down in priority. Chair lifts are easily doable but a pain to use. I have an external barn(?) that is now primarily storage. The many tools, gasses, and fuels in there are now inaccessable to me without serious finagling. The external house is frame construction and cannor bear heavy machinery. I have a solid shop, but smaller (read lighter) machines.
A wooden structure has some good points, especially when upgrading a little at a time. But a wooden floor is pretty much off the table unless it was built with some serious (as in rarely available) timbers. Construction and engineered lumber doesn't cut it for machine loads. 4x8 joists and 2x6 flooring as an absolute minimum. Then closely spaced piers. The weight has to be carried to the ground somehow. A preexisting concrete floor as a good starting point, and concrete (block) walls to boot, would be hard to pass up. Insulation is cheap when compared to load carrying.
I am not trying to hijack your thread, although it sounds like it. By describing my arrangement, I present some of the possible future scenarios that you might face. Conceeded, I don't mess around much with city codes and restrictions, building what I want where I want. But I do use some descretion in that building and make sure things look better than the neighborhood in general. Which isn't saying much, but. . .
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