Hey thank you all for comments and suggestions.
Well I don't think I will redo this image, mainly because there are a lot of other things I want to try out and the rendertime was over 12 h, so....
Naoo & domdib: Yes, now that you mentioned it, I realize the clouds are quite unrealistic. I kinda like them though, as I rendered lot with TG0.8/0.9 several years ago and therefore was happy to have some structured and fluffy 3D clouds here. ; )
It's hard to get nice clouds that let through enough light so that the right spots are exposed. Hope there is a way to do this via a painting shader or something (creating a little hole in the sky for the sunlight to pass).
Doswidanje
-Sen-