Glue XPS panels with perimeter foam onto garden fence wall

That means lime cement plaster and then the facade roughcast plaster on top, or what?

Correct. Lime cement plaster as the base coat and then the desired topcoat. This can be a silicate or silicone resin plaster.

I always use Baumit Maschinenputz KZP 65. It is very easy to work with and adheres extremely well. So far, only good experiences.

I have applied it both by hand and with a machine. Both work perfectly.