Hi, Jill. Realistically, vaulted ceilings in regular houses are a pretty new innovation. Certainly, some architectural student will come along and remind us of castles but most small housing has wanted to take all the advantage possible of the space under roof until vaulted ceiling came into fashion recently. So there is not a lot of historical precedent to look at.
Personally, I don't think that there is much reason for crown molding there, but it's your house.