Is it possible to use NOSTR to communicate privately with others in the world without depending on 3rd party messaging apps infrastructure or censorship (like Twitter, iMessage etc) in the event of a terrestrial outage or natural disaster taking out local internet and power or just access in general?

For example, can I host my own private relay using IP instead of DNS that only authorized NOSTR users can connect to that’s privately hosted using backup generated power and Starlink internet?