to configure ssh, it requires creating rsa keys, which in fact rely on the domain name. so you cannot configure ssh access without having a domain name.
no, by default it's blank. the domain name you configure on the router is local significant, it's not going to share/sync with any other device. so you can make up what you want.
one thing needs to be noticed is that the rsa key relies on domain name, so whenever you change the domain name on the router, you would have to re-generate rsa key for ssh access.
