how do I tell the machine to send piefed traffic to this subdomain and joplin traffic (for example) to another domain

You don’t send traffic to domains. You point all the domains to one host, and on that host, set up a reverse proxy like nginx, caddy, or traefik, and then configure HTTP routing rules. That proxy can run in docker. I use traefik and it does all the routing automatically once I add labels to my docker-compose file.

And only a 3.28 TB database? Oh, because it’s compressed. Includes comments too, though.

Off should be off. Airplane mode often leaves WiFi and Bluetooth on because airplanes allow them. And GPS doesn’t transmit anything, but if it’s enabled it’s still recording your location.

You can. But why wait for the weekend?