Is it possible to display the username instead of the email on the login page?
Is it possible to hide "Don't have an account? Register now." on the login page?
How can I force the user to change the password after a certain period of time since the last change?
Not yet. we have a feature request for that: Accept login using username/phone number in Login Web App
Not yet, also there is a feature request for that: Forbid new user registration via login app
There is no such feature yet, you can also create a feature request for that. We will keep implementing those for the upcoming versions.