I used to be that guy, faithfully rocking baggy skater shorts all the way down to 0F, below which I would don XC ski tights under the shorts. My shins were often raw, red, and seriously chapped by the time I got to work.

If you're gonna be dumb...

Congrats on the first winter commute! And welcome to the land of frozen toes. Given the temps that you're riding in, wool socks would be a good investment, as would a pair of shoes that don't breath (leather, or Gore-Tex. No running shoes or anything else vented). Personally, I find warm feet to be the greatest challenge to winter cycling, and more so than in winter running or XC skiing.

Where in both skiing and running your feet are kept warm through the physical motion of the activity, in cycling it feels like your feet are biomechanically ignored and left to freeze. This despite the amount of heat generated by the calves and thighs. For me, I start with a sock/shoe combo that is comfortable for walking an equivalent amount of time in the cold, and adjust from there.

As an emergency measure I carry a pair of Gore-Tex socks in my pannier, since they don't breath (marketing aside, Gore-Tex doesn't breath, or does so little so as to be negligible) they lock in moisture and heat. Back when I rode on the cheap, I used plastic bags instead of Gore-Tex. If you've got a newspaper subscription, save the bags that the paper comes in, they're narrow enough to not bunch up terribly in your shoes.