how many people currently living in New York City have the first name
Peter (& what are the sources for your answer?)

By New York City, do you mean only the 7 bouroughs. There may be no
easy way to get the number. For an estimate, I checked the first name
on pages 200 though 301 of the St. Cloud/Kissimmee 1997 white pages
and found zero Peter and zero listed with an initial of P. This is the
middle class and poverty suburb of Orlando, Florida which is perhaps
50% Hispanic. Apparently Peter is a less common name than it used to
be, and is likely becoming even less common.  Neil