What is the discovery process for these things like? What I mean is: if I buy 100 of them, put them in a room and turn them on, how do they work together to organize IP addresses?

Humans normally do this by "hi, I'm John" and "hi John, I'm Bob."

Do these things broadcast a MAC address set at the factory?

I ask because I think that when mesh networks become really interesting me is when they are entirely decentralised, as in finding a way for these things to have a universally unique MAC the second they turn on for the first time without some sort of authoritative server.