The *arrs work well with all of the big three, I have a Jellyfin install here but it’s apps for TV and what not are really lacking and attempting to get that to work with some of my elderly relatives I don’t look forward to. Just setting up Plex with them was a nightmare.
Yes, Jellyseer works fine but it’s really only a version specifially for jellyfin when OS already has support for it.
Gotta give it to you, you plugged away, learned, plugged away some more and got a really nice starting base for a setup. Now it’s time to start burning time and money on ever increasing space, a docker stack, a more powerful server (leaving the pihole to handle the ads), and on and on lol. Welcome to the hobby!