Sarah, I'd just like to second what Noreen said - it's fine, and in some ways desirable, to repeat dances within an evening.

Lucius, from my experience, you're right and wrong. There is a proper way to do the footwork in the ceilidh dances that has to be learned. But you don't need to do the footwork properly to have a good time. Those who are unknowledgeable need to know where to go and when, either by walking through the dance first or by having the experienced dancers giving them some verbal/physical guidance as they go along. But they can bluff the footwork and just skip or run or whatever.

Marion