For point 1)
you can’t expect a 1 to 1 fidelity at a far distance. Even with imposters the shadows would change. Most of the time this doesn’t really matter either because of the fog and haze also being an IRL thing that offsets or precludes those shadows from view. Unless you bake lighting you also won’t really see shadows from instanced objects at far distances anyway. (Not that that’s a good thing mind you, It’s just that the load on rendering becomes unrealistic for what little detail the shadows of something like a tree add).
Technically you could bake out a distance replacement material that includes the shadowed area if you are working with fixed light.
Either way, all of this kind of has 0 to do with what the OP stated… aside from the fact you can factor in and adjust the texture of the landscape to include those details at a distance by way of a render texture and a scene capture 2d component you only run once at the start of the pre-baked light level.