I would not rely on Nord’s VPN killswitch. It can be slow and unreliable and still briefly expose your IP to the swarm. I got an ISP letter thinking I was protected through nord’s killswitch, but turns out it was not completely covering me.
I would bind the client to the wireguard network interface directly through the client. In Qbittorrent you can do it pretty easily as @CrabAndBroom mentioned.