You need to install both. EE changed from 5.1.x to 5.2.x.
So, I'm guessing that I need to install EEM first and then EEPC?
2nd part of the question: This upgrade is being timed in conjunction with a move to a new datacenter to a whole new server...how do I migrate the 5.1.8 database to the new 5.2.3 server at the same time?
Yes, first install EEM, then EEPC on new server. Do not create database. Copy database from old server, point EEM to that database, upgrade file groups.
That's high level plan. Anyhow, you have "Endpoint Encryption Update and Migration Guide.pdf" document in EEM 5.2.3 "Documents.zip".
Also this link is handy: