First read through Multi-Material Layer Blending.

Landscape Blending with Static Meshes

Common height map resolutions in UE4. Courtesy Jan Kaluza

In the Material options, set the material's usage to "Landscape" so that it does not recompile every time it is applied.

Basic set-up of the material

Step 1: Make Material Function for Material Layers

Run outputs of individual nodes into “Make Material Attributes” then “Output” node.

Can separate individual outputs to use later in material node output. Use Material Layer Blends to blend layers together. Layer blend is key, and a blend should be used for each output.

Painting the Material

In the paint tools, make sure to enable "Weight-Blended Layer" like below. Select each layer to paint it separately.