Everything else just makes it easier to manage which depending on your preferences and how much content you’re dealing with that may not be a problem for you. I run the whole stack using Deluge as my downloader with a VPN. Radarr, Sonarr, and Lidarr automatically locate the torrents on the public tracker sites for me, send the downloads to Deluge, and imports the media into Jellyfin when the download finishes. I also use Jellyseer for discovering and requesting content, as well as allowing family members to request content. I also use Prowlarr to manage the trackers being used in the various arr apps. It’s a very robust and automated system but it all boils down to just downloading torrents over a VPN.
I don’t know enough about the fediverse or Lemmy code to say how easy or hard this would be to implement but if we’re logging in with the username [email protected] for example, it’s reasonable for the app to assume the server is located at lemmy.noogs.me and it can derive the likely URL of https://lemmy.noogs.me from that. The only case this wouldn’t work is if your instance is running on a port other than 443 because then we need some way to tell the app what the port should be.
Email (or at least Microsoft Exchange email) uses a protocol called autodiscover for this which uses DNS to tell an email client where to get connection information from, it then polls that URL for the information and configures the email client automatically. Using a similar DNS based approach may be useful as well.