2) that is entirely NOT true. You should install little snitch and see what happens even if you NEVER sign into icloud. note that the phone home contact is not immediate, it happens in the background at random intervals from random applications.
just some random services blocked by little snitch on a mac:
Tell me more about how dastardly it is that Safari communicates with Apple servers. Type it from your browser that doesn’t communicate directly with its developers.
2) I have booted macOS VMs without iCloud. I'm not sure of the nags though. I believe signing out of iCloud will prevent iCloud from contacting Apple.
https://support.apple.com/en-us/104958