Should i say how many years i've been playing an instrument or dancing on my acting resume?

It would depend what you're auditioning for. It would be good to put down all musical experience and all cles that you took. If it's just one cl taken over a long period of time, then you can definitely put years of experience down. Specifics are also very good, because people look for certain types of experience. Musical experience is ideal in theatre, fi you're auditioning for a show.