Well how much energy a surface will reflect is based on it’s reflective index and all objects have some form of reflectivity even though their index is super low. As examples a flash light will reflect more light than is imputed than say a brick which has a much lower index due to the uneven nature of the it’s surface so it’s a mixing of the 4 must have textures that creates a procedurally correct material. With out some level from all 4 there really is no way for a physics based rendering engine to accurately reproduce a real world result if your trying to produce a photo realistic render.
But for paint as an example keeping in mind that roughness is the same thing as glossiness I use
3 constant for the base color. Base color I usually use off white and link a larp to an off set color like blue. (splits the hue between night and day color proofing)
Specular with a low white gradient
Roughness using a texture I made in photoshop’s cloud render. I uses this for imperfect paint jobs that look a bit blotchy but a single constant will do the job for perfect paint.
I use a couple of different normal maps depending on the type of surface. A typical apartment celling will have a bumpy surface so high input for bumpy and low next to now for flat white painted walls.
You could decrease the input of roughness and the material will become more reflective but if you done decrease the input of the normal map then the result will be a reflective bumpy surface so to get it perfect takes a balance of all 4.
Interesting though PBR or procedural materials is not unique to UE4 so information as to physical based material construction is the same with all physics/photometric based rendering engine .
As for lighting techniques as a premier I found this to be an excellent lecture.
Did the entire video with out using GI or directly light and some of his techniques works well in UE4.
Now an opinion. I’ve tried substance and they are excellent for layered materials but found not so hot on large surfaces and have found making my own from scratch produces better results.