I start again (it became a mess).
Simply put, I'd like to sculpt with a custom brush on this level.
Problem is, it will be too high poly.
So what I'd like, is the following shape DECIMATED, with the normal map baked on it, and use that as a sculpting brush, and sculpt that details on the level in picture 1.
Just like a texture, but low poly AND with normal map on it.
But I just can sculpt the texture, in high poly, or just paint with the normal map, in 2D. I'd like both of the informations combined : lowpoly + its' normal map, in one sculpt brush.
Any other solution welcome.
I followed your instructions, but it leaves me with a simple normal map that will sculpt high details.
In fact, I want to sculpt low details (decimated) but have a superposition of normal map that will give the high detail, without poly counts. All of this in a sculpt brush. It seems it's not possible then.