Agree with most of what's been said so far. Don't have my RSCDS books handy, but the "original tune" for the dance is generally "the De'il Amang the Tailors".

The dance itself has 2 separate parts - basically

chorus (40 bars)
8x verse (48 bars)
chorus (40 bars)

Most bands would play "the De'il Amang the Tailors" for first and last tunes. with a selection of 8 similar ones for the 8x48. Try to keep adjacent tunes in different keys, have a few minors, and try to arrange for the change from 4th to 5th "verse" to be distinctive in some way - a "lift" either through key change, or familiar tune, or both. (That's the part of the dance where the "ladies in the middle" bit finishes and "men in the middle" starts)