Help! New to UMG/Slate coming from wx and Qt with OpenSceneGraph

I’m having a tough time getting started using UE with UMG/Slate. I’ve years of experience developing scientific visualization applications using wxWidgets and Qt to construct GUIs that work with Delta3D, OpenSceneGraph and OpenGL. I’d like to do much the same but use the powerful UE. The GUI creation process in UE is not at all intuitive and completely unlike anything I’ve ever done! I’d like to be able to create a separate window/panel with a bunch of control widgets that manipulate items that are in the the UE rendering window. Have open file dialogs for a user to load geometry models (i.e. .obj model files). How do I create basic button, text input, call backs (signals/slots) that I implement in code? To me, very basic GUI development stuff but not seeming to be very basic in UE.