Excellent progress, Jon! The rover looks great, and the scene like a frame from NASA animated footage. Maybe some more nor on the ground, or try using the Noise button on the mesh in edit mode (or maybe PET) to generate very slight variations in the terrain, just enough to break up the plane geometry. Maybe add a few stray rocks too.
Concerning the stars behind the sun and how to fix them from appearing too close, this can be dealt with in several different ways. Here are some possible solutions:
For static (non-animated) shots from a fixed camera position, the star mesh behind the planet(s) or sun(s) can be easily edited while in the camera view (press zero on the NUMBER PAD - be sure num lock is on). Select the mesh, enter edit mode, press the B key twice and scale the select to approximately the size of the planet(s) or sun(s), then press LMB to select the vertices behind the planet(s) and delete the vertices.
Alternately, vertices can be tweaked through PET so stars do not intersect with or appear too near to the planet/sun.
If deleting/moving vertices isn’t an option for whatever reason, for animated shots (and static shots too): a simple black and Shadeless Bezier curve circle placed behind and parented to a planet (with a Track To constraint to the active Camera if necessary) can literally black-out the stars behind the planet/sun. If there’s a lot of camera movement passing by the planet/sun, bring the Bezier circle closer into (even INTO) the planet/sun sphere so it doesn’t shift too far away from the planet as the camera passes (less of a problem though if the camera pass is relatively fast). The only other thing to make sure is that things are positioned so that no vertices (stars) move in front of the black circle so as to reappear around the planet/sun.
Lots of different ways to do this