Xcp-ng Networking and XOA Questions

I was looking into transition to XPP-ng, I like the interface. I do have questions in terms of how to manage them with XOA. I know XOA is a VM that runs on XCP-ng, however, if you have two servers, when you add the 2nd server under XOA, does it automatically migrate or do you have to configre High Availability? Or do you run an XOA VM on each physical server?

Lastly, how exactly do you safely shutdown or restart the servers. Thanks in advance