I strongly encourage the bicycle class, http://www.bikeleague.org for learning how to bicycle with traffic.
Join the local or state bicycle advocacy group to help you deal with the crap motorists dish out. I heard a lot of advice like "Don't let it bother you" as if it were a choice. If I could just flip a switch from "bothered" to "not bothered", that switch would always be OFF! But getting involved in advocacy was sort of like flipping that switch for me.
As far as sweating and being presentable for work, your sweat is more noticeable to you than anyone else.
As Thistle discovered when she biked to her meeting:
http://www.yehudamoon.com/index.php?date=2008-07-21
I sweat pretty easily, and I find the easiest results are when I wait ten minutes, then towel off and change into a clean shirt. For a while I had a shower available, and learned that I preferred not to shower even on very hot days.
If you leave that extra 10 minutes, and you are always 10 minutes early, then when you get that flat or other delay, you're covered. (Maybe you can surf the web or whatever during that 10 minutes...just don't get distracted because it easily turns into an hour!)
My goretex rain gear was a really good investment. In your area cold weather will be a problem and the rain gear works even better as a wind blocker. But it was expensive. I didn't get it right away, but either got a ride or got wet for a couple years! Put your change of clothes in TWO grocery sacks to keep it dry.
The other advice I have is to crystallize in your mind why you bike to work. That will help when you are pestered with questions, criticisms and judgments from people who think you are out of your mind. I don't mind those who are just curious, but some people seem to think that I'm the one making a statement about their driving because I choose to bike. Perhaps a guilty conscience?
I'm so excited for you!
2009 Trek 7.2FX WSD, brooks Champion Flyer S, commuter bike