Yup, with PIA the port is random but yes, there should be scripts out there to leverage PIAs forwarding with your torrent software. And yeah, if you were to port forward through your router that could lead to accidentally exposing your actual IP.

incompatible with port forwarding with any VPN

I’m not sure if there is a misunderstanding here, but port forwarding through a VPN is generally agnostic of most network setups. It’s a tunnel, doesn’t require your network to have port forwarding setup or even for it to be capable of it.