Hey I just got latter notifying me that I was waitlisted

I have a few questions though:
1) Does anyone know what percentage of applicants are taken from off the waitlist?
2) The letter at one point makes reference to people who haven't yet scheduled an interview. It would seem weird to waitlist people who are granted interviews even before they've had them. Therefore, should I consider this truly as a waitlist or some other kind of notification?
3) The letter says that a further decision will be made by the final round notification, March 22. However, I am planning to visit one of my prospective schools on the 25th. Does that mean I'd have to turn my enrollment form by the 22nd?