The folk thing is so important to me

Great! But in that case do think about who's going to be on in the first two or three nights, and make sure there's a decent proportion of no-messing bona-fide trad material. The way it is for the first few nights is likely to be the way it will be in the longer term - and if on the first few nights traditional material is an oddity, or not there at all, you're not likely to draw trad performers later on.