wow, your early to mid dec temps are like our mid to late sept temps....so having seen that, as a commuter in similar temps and also who has toured in these temps, just keep in mind that if its raining and cool like that, it can kinda suck. I ride all our Montreal winter, so cold doesnt bug me, but being out in mid 30s-mid 40s F or whatever in rain is pretty crappy, you get cold and miserable pretty quickly.
Cue the obvious points of having fleece, wool or whatever that will still be warm when wet and dries out well on your body, no cotton, but you know that from the military.

From experience, I personally have full rain gear, a good rain jacket, rain pants, rain booties so my shoes dont get soaked and freezing feet, even a helmet cover so my head isn't wet--but pretty much accumulated this stuff from "been there, done that" and not wanting to "done that" again, plus I'm an old skinny bugger who doesnt like being cold.
So, as a first time bike trip thing, hopefully you have some flexibility to avoid really crappy wet and cold weather--again, using the internet can give us pretty darn good forecasts, especially for two days, so it makes sense that if you can, to find at least a dry window of a few days. Things will be more pleasant and you'll enjoy yourself more.

have fun, that's the whole idea