I haven’t used it myself so I’m not entirely sure it’s what you’re looking for, but paisa might be worth looking into.

Is there a lemmy replacement for r/OpenSignUps?

In addition to plex you can set up software such as Radarr and Sonarr. This software can search for the media for you and you can set up quality profiles so you don’t have to worry about who specifically uploads; just that it meets your quality threshold.