You should keep that (rather nasty green) stuff off the cliff edge; it's floating. What you could do to make that rocky edge more interesting is, add a compute normal (somewhere), add a painted shader and paint the cliffs in front white. Use as mask for an empty surface shader after that compute normal and add some lateral billowy displacements in sizes 0.5/10/0.01, displaced maybe 25cm. You could also try an XYZ shader instead of the compute normal and add some fake stones mix to that cliff's edge in that sureface shader.
I wouldn't worry about skies before you've got the terrain in order.