I also started becoming paranoid, whether someone was collecting my data and offering them to “the highest bidder”
Debrid services do collect data, the recent RealDebrid drama seems relevant since this app is basically for use with those services
https://lemmy.dbzer0.com/post/32433831
It actually seems more private to self host Jellyfin to stream/playback already downloaded media files but that’s just my own interpretation.
That’s a tough one, if these are public torrents you may be stuck having to search for the torrents one-by-one and hope you can find their associated .torrent files to re-seed the torrents.
You do need a .torrent file, or bare minimum a magnet link to an active/non-dead swarm, to be able to re-seed torrents with existing data. Magnet links without any current peers on them are a bit useless for this task unfortunately.
If these torrents are from private trackers you can check the private tracker website(s), many of them have a feature to allow you to re-download all the .torrent files you previously downloaded from the tracker.