I'm not expert enough to comment on everything you've asked for here but I did run a torrent server on a pi 4 8gb, connected via LAN on 1Gb and it was terrible. The Pi just couldn't handle the connections and speed etc.,

Ran the same torrent server on an old satellite receiver (Dreambox dm900) with Linux (Enigma 2, Debian) and it ran perfect for years.

Would like to see if anyone else inputs on this as I wouldn't mind having it on the Pi really, if things have improved.