VPNs usually do store your IP when you connect to them, even if they delete it later (it is technically impossible to not know the IP address of whoever is connecting to the VPN). And the likes of Mullvad and IVPN do not allow port-forwarding.
I will repeat what I said to the other commenter: please read the documentation. Being a router doesn't mean that traffic and its contents can be linked to your identity. Data is broken down into chunks and encrypted along with metadata being scrambled. Unless there's a zero day I'm unaware of, you are perfectly safe.
Unfortunately, Qbittorrent's I2P support is still experimental. Assuming your seedbox provider can let you run BiglyBT or any other client that can cross-seed, all you have to do is add I2P trackers to your torrent file. You can also upload your torrent files to Postman on I2P for them to be registered.