A master material is a material with parameters for everything so that you can create nearly any type of material instance and apply it without having to recompile. To start, in your editor right click and check mark "Show Engine Content" to allow the engine content to be used.
*Note: Use a TextureSampleParameter2d (not TextureObjectParameter; allows attributes to be used) in the master material to set your texture inputs.
**Note: The color white is "1" and the color black is "0."
Any set-up for normals requires careful consideration of each channel independently, if adjusting it's value by another parameter. You may use the texture "Flatnormal" as a baseline in Unreal. The set-up for editing normals by 1 parameter (scalar in the below example) intensity looks like the following:
You should make multiple master materials for the various types of meshes and materials you expect to need (e.g., 1 for foliage, 1 for rocks, etc . . .).