I've been doing it in rochester since aught 6. Anywhere from 8 - 16 miles each way. Currently at 11-12ish.

Assuming you can't just catch a ride on the truly bad days, or work from home. Here's what I would consider necessary

1. Goggles
2. Studded tires, you can either switch them out as needed, or put them on at the first site of snow and take them off in march at some point.
3. Face mask for the truly cold days
4. Layers based on temp, my first few years I just layered PJ's over my shorts, worked great, now I actually have winter cycling clothes, better/less bulky then the PJ's, but an expensive initial outlay.
Also used to do fall/spring bike gloves with socks with the thumb cut out over them, now I have 2 different pairs of ski gloves.

As for things to consider, but aren't necessary:
Fenders
Disc brakes
water proof layers
booties

Your mileage may vary of course.