I'd strongly recommend looking at miglayout [0] if you have to do another UI in Swing (haven't tried it with JFX). It's pretty much the best layout library I've seen, bar none, for developing UIs in Swing. You can think of it of GridBagLayout on steroids, and it even handles things like reordering buttons on a per platform basis (eg. Ok and Cancel on a dialog are in Ok/Cancel order on Windows, Cancel/Ok on Mac).

[0] http://miglayout.com