From my experience using this addon I can say the following:
1 I do not use standard export, because it does not know how to fix dimensions in Unity.
2 The meshes is combined manually.
3 To get only 2 materials (Base + decal?) there are three options:
A. Discard info and panel decals
B. Use the shader created by Artem Zuev https://bitbucket.org/bac9/shading/overview
C. Write your shader
4 Decalbakedown Bake decals using as the base of the UV base mesh. It works quite well, but has its subtleties.
Here’s what I did using Decalmachine: