turorials tips on creation of outdoor scenes from artist perspective

I am looking for some links, tips, tutorials from the real aaa proffs on what is the preferred workflow of creating outdoor desert scenes.
Basically, I am trying to answer questions like;
What is the most common resolution of landscapes in ± 2km,
At one point do you add meshes instead of textures?
Is it true that the most common way of creating cliffs and hangovers, to stack models on each other? And if so, how do you process a large amount and a large world?
How do you deal with this? I have seen World Machine can create some real impressive terrains, but all that nice detail seems to be gone when you import this terrain. (i mean, import this landscape at 2017 pixels for a 2KM?)

Looking forward for any reaction.

regards! T

ps: I am searching the internet al over, too.