NixOS in isolated environment with Flakes

I was following this thread in developing nixOS in an isolated environment. I am relatively new to nix here and am facing a similar situation as the original poster and will have limited internet access. How could the current approach in the aforementioned thread be reconfigured with flakes and the new CLI? Are flakes similar to nix-channels? Any info on this topic would be much appreciated.

Why do you want to use flakes, specifically?

The original project I am trying to mirror to enable offline development uses flakes so I figured I would have to do the same here. Essentially, what I have at my disposal is a repo containing a flake.nix that is built as an overlay on top of nixpkgs. Would it be possible to do it with channels if this is my current setup? Else, I figured a translation to flakes would be necessary.