NEPSAC Elite 8, Large School, Small School...What deciphers the standings for these?
Is he Elite 8 the top schools based of RPI and the rest decided by size of student body? So if I look at NZPREP standings the top 8 schools there would play in the Elite8? Am I even close?

First of all, the Rankings, etc. for NESPAC is found on USHR. Elite 8 is the top 8 ranked schools regardless of size of school (enrollment). Large School are the next ranked Large Schools based upon enrollment, Small School are the other ranked schools found after the top 8 based upon enrollment.

So are the rankings different? Isn't it based of wins and loses?

https://www.ushr.com/neprep/jspr