Studded tires are an almost certain must-have if you are likely to be crossing any ice.
I have 7-speed IGH's on both of my bikes, and they sure are nice when the slop is flying. My commute is not very hilly, so I prefer them year-round.
Fenders and waterproof panniers, plus lights, etc. that you would want for all-weather riding anyways.
Bar Mitts or poagies on the handlebars are a nice addition to extend the temperature range of your hand gear another 10-20 degrees lower than otherwise.
I think bike type is less important and more up to individual choice. I do like an upright ride for ice, but it sucks when riding into those hard January headwinds.