@Jweiner It's really personal preference, based on your local weather and your driving habits. Real snow tires are worlds better than all-seasons in deep snow and on ice. Probably you know that living in WI.
I've never experienced WI winter weather, but from what I've heard I would lean towards real winter tires, specifically studless snow+ice category. Then for summer personally I'd use summer performance tires, but depending on your weather patterns and your own driving preferences, maybe you'd be just as happy with performance all-seasons that might last longer and could handle an unforeseen last storm or two if you switch too early in the spring. They won't grip or feel as good as the best summer tires, but you might or might not care about that.
If you run winter tires then for sure put them on separate wheels. Way easier to swap, and cheaper in the long run. Get 18x8.5" or even 18x8" for the winter setup, there's no point in anything larger. Not all 18s fit on the M3P, for example the base Model 3 18" wheels don't, but there are some aftermarket ones that do. Pick a tire size with a similar outer diameter to stock of course. I have 18x8.5" aftermarket wheels on my 2021 M3P right now, that are a direct fit, no spacers or centering rings needed. I'm using 245/45R18 tires on them.
When I used to drive in serious winter weather, and had a sporty AWD car, I ran separate summer and winter tires. I used that car's stock 18x8.5" wheels for summer, and I got a used set of its previous generation's 17x8" wheels for my winter setup. Switching twice a year was totally worthwhile, that car was amazing in the snow with the "studless ice & snow" category tires, and I had a summer setup with serious grip that was even good for track days, all on the same car.
That said there are places with mostly mild freezing winters where I wouldn't bother with real snow tires. Like the mid-Atlantic area. In those places I'd either run all-seasons year round (if I didn't care about maximum performance), or I'd use a snow-friendly all-season as my winter tire and still run real summer tires in the summer. Or maybe I'd use a "performance winter" tire + summer tire in those places. I used such a tire once before, it was like between an all-season and a typical snow tire. I think WI winters are intense enough to justify full on snow tires though...
