Complementing mobile hotspot with a 2nd OpenWrt device

I currently use my 5G mobile phone hotspot to share internet access to a number of devices.

This is impractical for a number of reasons. One being that some devices are wired-only; another that some devices require a constant (local) network connection, even if there's no internet access; the list goes on ..

I have an old PlusNet Hub One router (A sagecom model that supports OpenWRT), and I'd like to set this up to complement my mobile set-up. My questions is, how should I configure my network? I will still need to use the hotspot as a gateway to the wider internet.

  • Should I aim to have a separate subnet for devices on the router, or share the hotspot's subnet?
  • Should I use the router as a repeater? (Is this effectively the same question as above?)
  • How can I get the router wi-fi to both receive from my devices and send to the mobile (internet) efficiently? Won't this cause congestion?
  • If acting as a router, how will I handle the disconnection/re-connection to the mobile hotspot, when I inevitably take my phone with me when I leave the house?

In summary, I'm looking for a high-level overview, rather than specific config-file settings. How would I configure the extra router I have to maximize it's potential? Or does it even make sense to do this?

Thanks in advance!

WDS/ 4addr (the best setup) falls flat, as long as the mobile hotspot is not running OpenWrt (which is most likely the case). This leaves you with relayd (buggy, doesn't support IPv6 at all) or a routed client setup. It's possible, but not really good.

I've found this wiki entry which appears to fit my scenario: