So I’ve been looking around at Cel shading techniques in UE4. A lot of them don’t seem to support certain types of materials (specular, metallic, emissive etc)
I stupidly decided to try and tackle the problem myself…I’m a programmer but know very little about rendering and Post Processing.
However I have managed to get this far. Some things can be improved and extended upon…
I could potentially make the lights and shadows non-banded…maybe.
Bloom effect can be banded but tone-mapper needs to be disabled 
Metallic is kind of a hybrid, can’t see another way of getting it to work at the moment.
DoF just looks ****, I attempted to use the Scene Depth so there’s no effect on things in the distance so DoF would look decent, but it breaks particles as their not in the Scene Depth.
Probablly much more I could do but this is my first attempt at creating a Post Process effect, still so much to learn!