Hi lrathle,
In your mask, you only need to get the materials information (one color for the wood, another one for the metal). No need for several colors if the material is the same.
You should create your base materials (wood, metal, etc.) as classic textures (you don't need to have something based on your mesh).
You can do them procedurally or by importing bitmaps/modifying them.
Then, you can use a "multi material blend" filter (you can access it using the "search" bar of the library) to blend the different materials based on your mask informations.
Choose "color mask" in the filter options, connect the materials and select the corresponding color in the filter.