I said my needs. I was just sharing. Hardly understanding your normal use case of 10-50 users on a same kdbx. The best you could do is having multiple kdbx, fro subgroups of users. Since not everyone should have the master password to all those kdbx... But I am sure that if those were my needs I'd jump to vaultwarden too. That's why I specifically added the disclaimer sentences on my post. I didn't mean to rob vaultwarden of its value. Just pointed out the tradeoff. Your comments adds on to those tradeoffs, they're just different solutions with different pros and cons. The user who mentioned using vaultwarden behind a VPN gave great input, I wasn't considering that. Anyway, have a nice day.
You could first filter to a given tracker, select all torrents there en masse, and save some clicks; proceeding with your given steps. Cool! Btw, I use VueTorrent alt UI/ Theme
You want a bridge. Like Jabagram or Emulsion. But there's a limited set of features that will work. For example, reactions or group admin on telegram can't be easily replicated over xmpp. And, in any case, we are talking more about having messages and media on both rooms, on either side, replicated. That way, users on telegram (e.g. your friend) can talk to users on xmpp (e.g. you). Reliability for bridges is not good, there are glitches and messages that doesn't make it to the other side, whichever that is. I'd say you prefer to self-host xmpp with cherry-picked extensions, like snikket.org
Handbrake software supports many. Perhaps AV1?
I don't know which codec should be used to rip but you can pick whatever is in use by the latest and popular uploaders at whichever public tracker you decide on to use for those swarms
Check "green blue" deployment strategy. This is done by many businesses, where an interrupted service might mean losing a sale, or a client forever... I tried it sometime witj Nginx but it was more pain than gain (for my personal use)
Monetization is another secret probably. Ads alone could drive millions on streaming platforms. I don't have idea on public or private trackers, but I guess is also more than what I could win in my life xD but that's probably me just being poor.
As to how, I'd probably use zfs send | receive, any built-in functionality on a CoW filesystem, rsnapshot, rclone or just syncthing. As to when, I'd probably hack something with systemd triggers (e.g. on network connection, send all remaining incremental snapshots). But this would only be needed in some cases (e.g. not using syncthing ;p)
The protocol is called DLNA
There are two options, one is tunneling (e.g. tailscale, cloudfare tunnels, or a VPS either with special software or plain old SSH port forward constant connection). The other option, the most popular answer (I think, influenced by how yoy asked) is Dynamic DNS or DynDNS (e.g. duck, hurricane, freedns, etc.) this second one is like the classic solution.
The syncthing server only gives metadata (no files, only IPs) between the devices, so they can connect to each other. And it's self-hostable.