That depends on the mail server, but usually yes. The same mail server can handle multiple domains.

Yes. Email uses different DNS records than websites, so you can use your second level domain for both.

When you set it up, you’ll create MX records that point to your mail server(s), and A records that point to your web server(s).

Ok, let’s call it the sexyverse.

Email can work similar to Discord with mailing lists and chat apps like Delta Chat. Email is pretty awesome, but the big email services like Gmail and Outlook 365 are garbage.