Yep you can use your personal email address, this email address is for your admin account when your forum is set up
Yes they are, you will need email for your discourse forum to work (email notifications, account activation, etc).
The SMTP details will be with the email provider you’ve chosen, and also make sure to set up SPF and DKIM records as the install guide says. Your email provider will have instructions on SPF and DKIM (it involves going to the place where you bought your domain name, and creating some TXT records).
This is for setting up HTTPS, you can read more here:
I don’t know too much besides having followed the install guide myself and helping a friend, so others can correct me