If you are dancing all day: high waist, every time. It sits at your narrowest point and stays there. A low-rise short spends the day being pulled back up.
If you are going to be sitting on the ground: avoid heavy sequin on the seat. Sequin backing digs in after an hour on grass or a curb. Lace, lame and plain holographic finishes do not.
If you want more leg without more heat: chaps over a short. It is the fastest change you can make to a silhouette, and it costs you nothing in airflow.
If cheeky is more than you want: a mini skirt with a bottom underneath. You get the same length with a layer between you and the crowd, which matters more in a packed tent than it does anywhere else.
On sizing: size for the waist and treat coverage as a separate question. Cheeky is a cut, not a size. Getting the waist right and then deciding how much you want on show is the way round that works.
On building the rest of it: match the waistline first. A high waist wants a top that ends above it. See festival tops, and accessories for the belts, harnesses and leg wear that finish it.
