Wow I had not heard of this. Thank you for sharing. It says lighthouses are optional but recommended. Any idea how it can work without a lighthouse?

Haven't used, but I believe lighthouses are primarily for host discovery (dns) + hole punching. I think if you configure static hosts on all nodes you're good:

https://www.defined.net/nebula/config/#static_host_map

That's correct.

Yes nebula is amazing, I'm using it everywhere! I made a rest API to manage nebula lh, multiple networks, users, certs. All packaged as a docker image. And open-source of course: https://github.com/elestio/nebula-rest-api