Multiple Layers Help!

Hey everyone I was hoping you could help me with setting up multiple layers on a landscape to paint with. I know there is a great tutorial for a very basic version of this but I was wondering if there is a better way to do this so I could use Materials already created on the Market Place. I just got the newest Landscape Material Pack. With that I would like to use the Materials in that pack to paint on a landscape. With those mats I want to still have the the roughness and world displacement and so on to continue to be in use. Can anyone tell me how to do this? Thanks so much in advance!!!