I know they do the open dance floor thing at sikh weddings. Dances in general should be kept for a smallish, close mehndi, where they people attending are people you personally know.
I don’t know, I think it doesn’t hurt to get a flawless skin for mehndi/nikkah. Maybe not go OTT with the rest of the face.
And yes! Does no one do actual singing at mehndi anymore? That’s the best part of the mehndi I think.