I used the fluffy clouds material in volumetric menu. I am using B5 btw, so you will have a different set of menus to me. The trick is to edit the colours of the cloud in the mat lab.

I just changed the ambient and diffuse colours to resemble the image you are recreating. The problem you may have is that your sky is different to mine so interaction may be different. Looking at your water I would turn the specularity of that mat down a bit then the light reflection would not seem so harsh.

Other things to consider is adjusting the camera angle, make the terrains further away but bigger. The scale of the water waves suggests the terrains are too close compared to what you are trying to portray.

I know that sounds like I'm picking on your efforts, but I am impressed with how far you've come. When we all started out it seemed like a nightmare. Like a child learning to talk!

http://joevinton.blogspot.com/