I would say the benefit of OpenSUSE is that everything is preconfigured to work right out of the box, including btrfs snapshotting with snapper. Once you boot it’s time to download apps, and go. Very windows like for those who just want the system to work. Updates are one click.
I think you are definitely getting into overkill territory here with a server rack dedicated to Plex and a GPU. Most igpus on Intel chips can transcode 10+ 1080p streams and 2ish 4k streams. Unless you have 100 users seems over kill to me.
Edit. I’m on Unraid with about 30 users, and I only give Plex and all my other containers 6 cores from an i7 10700k.