I don’t think think I have considered rTorrent before. But this one doesn’t have a remote GUI client the way deluge and transmission allow their UI to connect to a remote daemon, right?
Correct. You're referring to the thin client, offhand I think it's just Transmission and Deluge that have that. You don't need a thin client for a headless torrent client setup, plenty of people do fine with a web ui. But I get it, if you prefer using a thin client then yeah Deluge or Transmission are your options for that.
re: Deluge once you have logging enabled it'll be easier to troubleshoot things. Always seemed a bit odd that Deluge doesn't at least enable error/warning logging by default but that's a Deluge thing.
No, you'll torrent fine via I2P without port forwarding. Note that the torrents are running through the I2P network so technically you wouldn't want to open your torrent client to the clearnet anyway. It'd be like purposely introducing a VPN leak in your VPN setup by allowing it traffic outside the VPN (or in this case I2P).
Been a bit since I've tinkered with torrents over I2P but for a while I was seeding torrents over I2P and would get pretty good seed/upload speeds to other torrent peers. Was mainly testing with i2psnark and BiglyBT.
Fun fact: Torrent hashes don't change, so that same exact torrent you might download at TPB or wherever would still download within I2P as long as there's someone seeding it there.
Also see https://geti2p.net/en/faq#ports
Not exactly what you're asking but you can open a port forward for I2P itself to better communicate with other I2P routers. "routers" in this case usually means other people running I2P.