I’ve not approached UI this way, so maybe there is something out there already, but since you want the elements to react to the world, I think 3d geometry would be the simplest. It looks like you need to know mouse position for clicks and that’s accessible in bp anyways.
Maybe all of the elements could just be modeled, including the gold trim. The text could be controlled with text renderers which exist in the world, but I don’t believe they are too flexible, but maybe enough for your goals.
In Unity, UI exists through a different camera - I think this is what UMG serves as, but you’re essentially after something like that while still receiving light of the environment. You may want to experiment with SceneTexture nodes for Post Process effects. There is a Specular choice which references lighting info, so it technically doesn’t have to exist in 3d, but defined by material and set up in the post process volume or your camera.