No. Due to the structure of GeoSim and Blender's shaders, each planet is restricted to being illuminated by a single sun light, and cannot receive shadows cast by other objects. If these are required for your scene, it is recommended to use native volumetrics.

No. GeoSim is soley for rendering photorealistic atmospheres and clouds, along with detailed terrain displacement. All textures, aside from the included earth textures, must be provided by the user.