Hi all !
First of all thank you for your reception, your feedbacks and your encouragements!
For the shadow density, I wanted from the start something quite dramatic and contrasted, but realised that my screen isn't well calibrated. On my screen it is not so dark, I may try to finalize my image at work on a better display, within nuke (I just tried the render passes and it works very well!).
I did the church in Maya, and the river is from a draw I did in Photoshop. I used it as displacement with an image map shader.
Thank you Oshyan for your references! I am agree with your advices and am trying to do my best. A lot of testing (and waiting), still not have what I want.
My main problem at the moment is the render time, it is hard to work without fast feedback... (and it is longer with render passes). I render one image each morning, and sometimes it isn't ended when I come back from work (the last one took 14h with render passes, atmo quality 32, there is 9 3D clouds nodes at 0.4-0.6 no acceleration, detail is 0.65, AA 7). I may consider to lower these settings and de-noise some of the passes in nuke...
The ground part is very long to calculate, maybe AA 5 can be the solution, I will try it tomorrow.
Here is my last iteration, still need work. I am not satisfied with the ground just after the river (actually I preferred my last version for this zone). I am not sure with the snow, I think I should add more on the top, or remove it. And I don't like the grey rocks after the church. I am still thinking of adding a foreground rock, and maybe something to look at behind the lake on the right, where the eye is attracted....