I would use FXML and make multiple scenes. If you are not to sure on how to handle multiple scenes, I would suggest you goto the following two links and read over them.
Angela's Blog
getting started with javafx
I myself made a login screen based somewhat on those codes as well as another one that I cant remember at the moment, but how I went about it is as follows...
Key parts in my main class are
This is only part of the code I have used and is also only from my main class, but what I have done is when the program starts it does the gotoLogin first. The login screen's controller is made aware of the main screen via the method shown in Angela's blog, and when a user successfully logs in the controller calls on the main screen's method of gotoClientHome and pass it a user object. In your case you would be passing the information that the user had entered.