I've been flirting with taking the plunge for a little while and my opinion is, if your just starting out and you don't have the gear, or feel your not prepared, reschedule. Wednesday is supposed to be a lot warmer (I'm in MA too).. and from my experience, if your just starting out in something, and your not comfortable, its hard to keep the motivation flowing. There is of course the danger of making perpetual excuses, so if your afraid of putting it off, don't...

Here is a pretty good video for how to dress for subfreezing temps... FWIW, your body generates a lot of heat when you are cycling, so it is very possible to over dress for the temps...

http://www.youtube.com/watch?v=8i7vcboSje0