Are there any musicians out there who have played for contra dances and can give me some background info on what I'd need to know to play?

There is a local contra dance group who is always looking for bands. I've got a fella who is a beginning/intermediate fiddler, a guy that plays tin whistle, and I can cover either guitar or banjo. None of us have ever played in front of a mic. All of the local experienced musicians "have better things to do" than tutor the lot of us (or even any of us individually).

I know we need around 20 tunes. I know we'll have to play the same tune for up to 15 minutes at a stretch. I know we have to keep a constant tempo throughout the entire song. What other things are important to know when playing for a dance?