Went to the Disney concert. Powell is handicapped-accessible with elevators just to the right of the incredibly beautiful foyer. Any usher will help you find your seat and will get you to the right level.
This is one of the most outstanding concert halls in America. The acoustics are superb and seating is wonderful. It is a jewel for St. Louis, and I recommend coming to hear any St. Louis Symphony concert for a great evening or morning concert!
There are several free concert opportunities that I've used: the 50 Free program; Onstage at Powell, and various venues around town like in Tower Grove Park. Check their website, it's amazing!