I actually just purchased a set of winter tires and wheels off tirerack, but I went with 15" steelies and 195/65R15 Michelin X-ice 3. The 15" tires are cheaper and are narrower so will cut through the snow better. I'm out in massachusetts, and when we do get a winter storm, the plowing jobs aren't the best. Some other states have a much bigger budget for snow treatment than we do.
Next, I didn't really want a set of nice alloys that are going to look dirty from all the salt, sand, and road grime during the winter. I don't wash and detail my car that often, so I only think its worth buying nice rims if you're going to keep them clean. Just my opinion.
I think wheel covers look tacky, so I'll just keep the steelie look, but I would be interested in some sort of center cap to protect the exposed hub. Any thoughts on where to find something like that?
Back to the OP, my two cents would be to analyze what kind of weather you drive in during the wintertime. If you must drive in deeper snows, I'd recommend downsizing to the 15s for winter. But if you care about the look and don't need to get around when the snows are deep, then 16s will probably do you ok. I'm just more of a safety over looks kind of person. But any winter tire is way safer than an all season tire in your part of north america! Regarding rims, steelies are cheaper and you don't feel as bad about them if they get beat up, plus you can always use a wire brush to remove rust, prime, and put on a coat of spray paint if you need to. Again, if you are greatly concerned with the look of your rims, I think aftermarket alloys are the way to go. Just as good a quality as OEM, but without the extra costs. I'd clean the heck out of them though. When I had a toyota tundra with alloy wheels, 5 years of Upstate NY weather wrecked the finishes on them.
Just my long-winded two cents.