The nice thing about Jellyfin is that you can point Jellyfin and Plex to the same media folders and both will work, to try it out.
I would get a Synology with intel Quicksync if you go the Synology route for hardware transcoding. Unfortunately, a lot of the new models don’t have it.
I just have a 220+ but would maybe get a 4 bay model if I did it again.