You might want to check out the self-hosted communities on Lemmy for more info.

If you want to use Cockpit, the 45drives Cockpit modules make dealing with SMB easier. I think TrueNAS is a better option. If you want more flexibility, then Proxmox VE is a popular choice.

I think I’ve seen this one before.

If you’re not using a VPN, it’s possible your ISP is throttling your connection when it sees p2p traffic. Just another thing to look into.

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.