I think in your case it really comes down to transcoding the streams. If your player doesn't support a video format, the Plex server will have to transcode it into a format that's viewable. A pi might not be able to handle multiple transcodes at a time.
I personally use a Synology nas for my server and haven't had any issues, but can be expensive.
Elmo seriously sent that to everyone in the company? When that information was maybe relevant to a handful of people?