Making good terrain

(1)Hello, i am trying to make a half descent terrain. so i add plane and sculpt it how i want it to look, using the sculpt mode. I then add my texture. the texture then stretches over the whole landscape and looks really dumb. So i try to do it usinf Uv image editor and face select. But since i had subdivided my terrain and sculpted it, it has tons of little faces. How do i add or paint on textures and still have it look good?
(2) I also am wondering how to add images to a certain place on my model. EX. say i want to add a cool decal onto a car. How do i do that?
Thanks for anyhelp you can give me.
(sorry for spelling mistakes, i was rushed)

FIrst of all, about the UV unwrapping, if you have too many faces to unwrap it, you should’ve used multires. But as long as there are no overhangs, you can use project from view in top view, which is way faster but will make steep areas low res when you paint them. If you want infinite resolution, you can use a squished procedural clouds texture to make it look canioney, but I don’t know what material you’re going for, so you decide.
Secondly, about adding decals: add an empty with the z-axis pointing opposite the way you want the decal projected, then in the image tab of the decal you want press “clip cube”, and in the texture input tab for the decal select “object” and type the name of the empty. scale the empty to change the image size.

Hey, thanks for your help i appreciate it!