2 - What happens to my guest account when I log in with Facebook?

You will still have your guest account and still be able to use it should you ever decide to disconnect from Facebook.

However, if you see this pop-up below, you are trying to log in with a Facebook account that was previously not connected to this guest account on your device. This will, in turn, overwrite the guest account you currently see.

Logging in with the original Facebook account that was connected to this guest account will revert the overwrite.