Hi Bob!
Cool work, looks very good so far!
Agree with Moodflow about the color variations. You might also try to add some extra bumpy details to the flat surfaces, especially on the right.
I like the soft clouds and the tree-models. They don't draw too much attention, good!
I think adding the fill light was a good choice. The lighting looks quite good now, however the color-toning is a bit off in the lighter shadows. Perhaps you've changed the "soft clip effect" in the renderer node settings?
It's not really disturbing, just wondering.
Martin