Rushfest is a contra dance to DJ'd music, often with colorful laser lights.
There isn't usually techno. If there is, it's one song out of 30 or more that make up the evening. It's not constant OONTZ-OONTZ-OONTZ you get with techno.
Everything! Top 40's from the 1950's to today. Pitbull, Journey, Beyonce, Frank Sinatra, Kool and the Gang, Kesha, Diana Ross...
You have my full and explicit permission to wear whatever makes your heart happy. And that is comfortable. And that you can sweat in.
People wear anything from cute skirts and dresses (for anybody) to leggings (for any body, especially yours) and tank tops, to shorts and t-shirts.