A few weeks ago it was -5 for about a week straight, and I commuted every day. The first day was an experiment, and I overheated. I'd say snow pants are too much, as they are meant to keep you warm even if you're sitting in snow. For me, two pairs of gloves, two pairs of wool socks, some long johns under my pants, and a shirt, sweater, and light coat are enough. Something to cover your ears and eyes is definitely necessary, or you'll have a sharp pain at the ridge of your nose that is not fun. I don't usually cover my face, but I have a beard, so it's not needed.
Good luck! After you've done it a couple of times, anything over 0 is easy and not worth dressing fancy.