I'm not terribly far from you and have a pole barn that has a climate-controlled side and one that's just storage with open air eaves. I very quickly learned that large metal items on the open side will flash rush in hours when there's a warm Spring day with a big temperature swing...it's a huge hassle. Coating things with Fluid Film or ATF helps, but I've seen them sweat under the Fluid Film and develop rust anyway...not normally, but it can happen.
The other problem with having to coat your machinery is cleaning them every time you want to use them...not the end of the world, but one more thing to deal with.
For a garage like you're talking, I would look hard at a mini-split AC with a heat pump function. They use very little electricity and aren't terribly expensive. The climate-controlled side of my shop has a mini-split with heat pump I run for most of the year. I also installed a radiant system in the floor for the coldest part of the winter..usually just late December through Feb. The mini-split works well down into the teens, but then can't keep up and that's when I turn on the radiant system. There are some hyper-heat models now that go down into the single-digits. Since your garage is attached, it's better from a heating standpoint than a stand-alone building, so that's a plus. I'd be a hyper-heat system would be enough for where you're located.
Most months my electric bill for the pole barn (has its own meter) is under $50....that's running the AC/heat, machinery, welding, etc. Beyond keeping the machinery from rusting it certainly makes working on projects a lot more comfortable, and makes it easier to focus when you're not freezing or melting while you work.