probably posted on mastodon as well

everything should be behind a firewall

This is possible, and exact directions will vary on distribution of the vm client. I personally do this but with split horizon dns and dnsmasq on a vm.

impossible to leak is where it gets tricky, and that will require an understanding of networking in your distribution. there will also be tutorials on this, but it’s very easy to mess up.

the idea with qubes is that whatever you are doing with tails would just be done in a tails/tor qube (vm), which are/can be amnesic.