As to your overall issues, I made a little demo project that hopefully should help you. There is no code, just some project settings and the scene tree.
(Please note that I do not have rights to the background image, so please do not reuse it. This is just an example.)
Generally for mobile dev, the direction you want to expand or shrink is the longer dimension. That will be X in landscape or Y in portrait. This is because that is the dimension with the most variance, both in aspect and in resolution. When testing landscape, rather than squishing down the window in Y, extending the window in X will give you a better approximation of how it will look on wider devices.
