Roughness is essentially the same thing as gloss (though sometimes mapped to an inverted scale). Metalness is pretty common, for example UE4 uses metalness, not specular maps, so I would say its very important to understand how to use both and the differences between the two.
I will definitely put some windows there! I have a bad feeling that Marmoset is not the right engine for complex environments and I´m waiting UE4 so bad :) Marmoset is awesome for rendering small things with beautiful details but example multiple dynamic lights will make the scene heavy and this scene will have a lot of…