1) No. I knew a few people last year who were interviewed and eventually rejected without being put on the waitlist. Those people admitted to having pretty poor interviewing skills which probably played a part in that decision.
2) No clue what the total number is, but people are interviewed throughout the year so as people turn down their seats, people are taken off the waitlist and the fresh interviewees are added on, so it is definitely a large number especially considering how many seats there are to fill.
3) See #2. There is probably some kind of priority assigned to applicants as well, but who knows?
4) If NYU is your #1 choice, let them know. NYU makes it very clear that they want people who WANT to come here. Call Dr. Mejia and and tell her that you are on the waitlist and that NYU is your top school so you will accept if given an offer of admission. Make sure you tell her your name and application ID so she knows how to pull up your application. I can't promise you that this will move your name up on the waitlist, but there are a lot of anecdotes on SDN about people calling for this purpose and being accepted soon after.
