Materials / Shaders: What does and doesn't go well together?
I heard that it's not advisable to have a shared material/shader for some types of surfaces (e.g. metal and skin) because they both require entirely different setups.
Now I'm working on a car and wonder if and how I should separate it before I do the textures?
It mostly consists of metal, glass, rubber and leather.
My idea was to have one UV space for metal, one for glass and then just put the simpler stuff like rubber, leather and dirt in the same spaces, wherever they fit and end up with 2 material slots on 1 object.
(Can simpler stuff like rubber and leather go on the same material or do I need another material slot just for that?)
It will be rendered in Marmoset and Unreal and I'll use Substance Painter for texturing, if that matters.
Really looking forward to any helpful comments or links to tutorials, because I didn't find anything (might have used the wrong keywords).
Thanks! 
Replies
Metal, rubber and leather could all use the standard shading model and be opaque or masked if need be. I don't think Leather has enough typical cloth characteristics to justify the Cloth shading model. Then again if you're referring to the car paint metal, you could split that off into another material and use the more physically-correct Clear Coat shading model.
Glass would use the same Standard shading model and would be Translucent.