Emails are personal data and are not allowed to be shown without specifically opting in for it. In Europe at least. Same for IP. This is also why when you "Recover Password" it will say something like "if this email address is found we'll send you a mail". So nobody can just check if an email exists on the service.

Depends on your personal acceptable levels of spam in your inbox, I suppose. Thus the common "junk email" and "good email I actually use" scheme many people today rely on. One of those emails I'll give out, the other is a closely guarded secret only available to a select few. I actually have a middle ground too of "not junk, but I don't know these people IRL," too.

It's hard to find an email service that doesn't ask for a phone number now a days. Even shit ass Proton mail does it now