Hey, this my desperate try to finally realise my idea.. hopefully some of you guys can help

And sorry btw. if this is unfitting for the forumstructure, but i couldnt find a better place to post.
So i bought RaceTrackBuilder a few months ago being fascinated of building own tracks on
Assetto Corsa, but got stuck on the same spot as this time. Basically, i want to use RTB to make a "ruff" version of a fantasy track i have in mind for a long time now. Using the Tools to build the terrain and the road itself, and then ... i guess convert it to something like blender to make it "pretty" because RTB itself isnt that good for putting in objects and stuff ?
I honestly dont have that much of a clue about modding, i did a bit of modding back in the synetic games days, and a few months ago for some basic charactermodelling and animating in blender.
But my mainconcern right now is something fairly simple: How the hell do people
texturize their maps ? a really basic example: if i want to make a hill next to a road, how do i get a proper stone (ish) texture on it ? The whole internet is filled with Tutorials about the Google Maps method, and how to model a road in blender, but it
seems theres just no tutorial or step by step guide about making a
fantasy track and actually
texturing things


Im fine with people saying me what i have to do next or what wont work, but i
need to get a clue about what i have to do to get this idea
OUT of my head and dont get stuck on the same point everytime..
And yes, its not a race track, and yes, the idea of making a big "freeroam" fantasy track as a "firsttimer" may seem weird, but well ... thats just the way i work. I am the guy who draws all the details before he starts with the lines.
so my queston would be:
is it makeable as i think of it (using RTB to make a ruff version maybe with proper textures and then continue elsewhere) ?
How do people texture their maps ? I know i can somehow change up materials on RTB, but i dont know if thats the proper way... it just doesnt seem that good to use, with just 4 textures usable and a brush tool that is just inaccurate.
So yeah, as i said, looked hours of forumposts (and yes, i saw the "basic guide" as well, but i dont think it fits my problem very well?!) and trashy videos about RTB, but i still dont know how proper to texture my little hill walls next to the road or put in houses where i want them to be

for example: RTB is not the way to go, and i should just make the terrain and the track, export it and texture elsewhere ? fine.
i just need a clue (its driving me crazy) 
thanks for any answers in advance 
Greetings from Germany,
Norman