Hi - I'm from the other Portland (Maine) and I ride all winter (at least once or twice a week if at all possible). I don't ride when it is below 10 degrees or if the roads haven't been plowed. I do switch over to my mountain bike in the winter even on the roads because of black ice, pot holes, etc.

All the gear you mentioned seems appropriate but you didn't mention what you are wearing on your feet and hands. These are the two areas that I find I can get uncomfortable. I have some heavy duty gloves but others I know wear two layers (liner and glove) and some even use heat packs. I also wear shoe covers over my shoes and when it is really cold will use plastic bags over my socks. I love "woolie boolie" cycling socks.

You don't mention what else you do for exercise but I'd suggest starting out riding two times a week (plus a weekend ride). Check the weather forecast on Sundays and pick out the nicest couple of days for the week. Another option, to build up your endurance, is to drive into work one day with your bike, ride your bike home (if you can leave your car at work). Then the next morning ride into work, drive home.

Let me know how it goes.