How do you create a splendid background mountain?

How do you create a background mountain like t$$anonymous$$s?

There are some basic question about creating a scene like t$$anonymous$$s.

1. shall I use terrain texture or grass mesh to build grasses? If I use terrain texture, it will be lack of stereoscopic feeling, and the repeating texture is really hard to eliminate. If I use 3D grasses, it will cost so much and it will be culling if the distance is far from the camera (also happened to 2D texture grasses). And HDRP terrain system does not support 2D detail painting.

2. The mountain trees have the same problems with terrain grasses, too many trees cause low performance, even though I use LOD trees.

3. If I only use one type of LOD trees and one type of grasses (LOD or textures) with different colors in a 1024 * 1024 terrain like the photo, how many batches and tris should I control if I want the FPS ac$$anonymous$$eve 100+? Is it possible to do that?

Thanks!