The only real constraint here is VPN port forwarding. You would need a VPN provider that supports that in order to hit DHT swarms. So, just make sure the provider has that.
As for kill switching, run the VPN and torrent client through docker. There is probably already a docker image out there that does that depending on what provider you go with. Essentially what you'd be doing is sandboxing your torrent client and then only passing in the VPN interface via docker network to that client. If the VPN tunnel goes down there is no other egress point off the network segment and zero chance for traffic using a different interface.