https://www.smashingmagazine.com/2020/01/complete-guide-wordpress-multisite/
https://pressable.com/what-is-wordpress-multisite-and-when-should-you-use-it/skylightpaycard
Also, should we use subdomain or subdirectory?
Personally I would prefer a subdomain, but really it’s a personal preference. It doesn’t make much of a difference from a technical perspective. Subdirectories ***may*** be easier to manage when it comes to server setups.
Buy a new domain, set up your multisite configuration, password protect it, dump in a theme, and add a handful of sub-sites in order to test and make sure it all behaves the way you expect.
Everything is very open with a clear description of the issues. It was truly informative. Your website is very helpful. Many thanks for sharing!