It can. For instance I have a flake where I define all of my machines, share some confit between them and have clearly defined customisation points.

Form that configuration I can build everything on one of my machines and push the builds to the others. Or each machine can do its own builds.

Have a look at projects like NixOps or Colmena to see some more automation on top of standard builds targeting other machines.

Sure. I do this in my homelab with ~20 devices, most are very small/embedded, a few are bigger including the build machine.

Depending on your specific requirements, yes. And quite elegantly.

There are several ways to do this. For one, see: https://github.com/nix-community/colmena