The C64 Mini and C64 Maxi are readily available today and affordably priced, making spare parts easily accessible.

If those work well enough for them, I cannot see any benefit of upgrading.

Is this the most recent Kingdom Come 2? I’d been thinking of getting it myself

No, first one. 2 has not been released yet.

Kingdom Come Deliverance. Low fantasy, no map marker (in hard mode), no superhumans or anything too fancy…

Can you access your wan ip when you are somewhere else than on your own lan?

If not, then this is probably just that your router does firewalling and nat is such order that you can access admin interface from local network via wan address.

If yes, then router has some serious misconfiguration.