how likely is it that i get my top location preference as a new grad software engineer?
As a new grad it will be tough. Interview as early as possible to get the offer before headcount fills up.
That won't necessarily help. We know how high the demand is so the bar is unlikely to be lower just because you interview earlier (and the top interns are first in line.) If your goal is to stay on the East Coast as opposed to NYC in particular, Boston is also hiring new grads and should be easier.
NYC is the second most selective of the major Facebook engineering offices for new grads due to demand exceeding supply of positions. Good luck!
What's the first most selective?
London due to even higher demand due to visa policies in the States.