Thanks for the feedback, I really appreciate the vivid and friendly community here!
Zaxxon, that's a wonderful painting. Thanks for that, didn't know the painter and his work.
What I am going for, hence the term photo-real, is a believable atmosphere, and some drama of course. I don't think the image won't have the intended impact if it lacks natural (and photo-real) lighting and clouds. However, I totally agree when you say that 'photo-real' and 'natural' aren't necessarily the same thing.
I went back to the initial lighting, only need to do some tweaks on the foreground terrain, grass and rocks.