Hi Martin Rees,
When a user tries to access the page and it is not registered, it goes to the ExceptionHandler which will redirect the user to Login. By default, the parameter OriginalURL is used as an input to redirect the user to the page he was trying to access after logging in successfully:

In your example, when the user is redirect to Login screen on the OnException handler, the OriginalURL should contain the same link as the email.
Regarding the second question, you can have a parameter on your screen ActiveTab that is filled on the Tabs input parameter with the same name:

In this way, you can control the tab to be opened when redirecting to a screen.
Regards,
João