Before you move to Linux, have you had a look at OpenCore Legacy Patcher? It will allow you to install newer versions of MacOS on your unsupported MBP. Mr Macintosh’s channel on YouTube is a good resource for this.

Have you considered other approaches, such as Tailscale or Cloudflare Tunnels? I think you’re complicating things.

I have some SmartThings plugs that work similarly, I think they have a UK version.

TubeArchivist sounds like a better fit for that.

You can use lists in Readarr. Set up a Goodreads account, link Readarr to a list in Goodreads. Any books in the list will automatically be added to Readarr.

Jim’s Garage on YT, he recently did a video about running Docker in an LXC. I think you’ll find the info you need there. It can be done, but if you’re new to Docker and/or LXCs, it adds an additional layer of complexity you will have to deal with for every container/stack you deploy.