This is a great writeup! Perhaps I can put in a plug for the create_ap script which I have been maintaining for many years (http://github.com/dlenski/create_ap).

It's a shell script that allows you to turn any ol' Linux computer into a WiFi router in one quick command-line:

By default, it will setup your WiFi card as an access point (allows WPA2/3, MAC filtering, etc), setup packet forwarding and routing, and run a DHCP and DNS server. It will generally pick sensible defaults, but it's also highly customizable. If your WiFi card supports simultaneous AP and client mode, it will allow that.

Its requirements are extremely minimal: basically just Linux, a compatible wireless card, and a few common configuration packages (hostapd, iw, iproute2, iptables, dnsmasq). No NetworkManager needed.

I used it as my own home Internet gateway for many years, running on an ancient fanless Atom mini-PC.

Because it can quickly setup and teardown WiFi networks on-the-fly, it's also a valuable tool for setting up test networks when reverse-engineering IoT devices. I use it frequently for this purpose (see https://snowpatch.org/posts/i-can-completely-control-your-sm...).