Commute to work in Chicago, 8 miles each way.
It's not that complicated. You get very warm while pedalling; it's like a fireplace in your belly:). You can try various light layers as your going along (winter sets in kind of slowly...).
I cannot emphasize enough: Don't skimp on lighting. I have a powerful tail light, a powerful helmet light, and a super powerful handlebar mounted high intensity light. All USB chargable. If you're riding everyday in the winter, get good stuff. It's freagin' dark in December!!
Personally, I wait a couple of days after it snows to ride (gives the plowing/salt/melting process some time) and don't own snow tires. I broke my rule one day last March and spun out on some black ice (luckily just bruises...).
A balaklava (spelling), some lighter weight gloves (35-55 degrees) and some super warm gloves (<35 degrees) will be needed.
Pearl Izumi stuff, while expensive, really holds up:)