Hi and welcome to the forum Stephen. I had a quick look on here -
Tamiya Color - Acrylic Paint
And I think possibly XF-56 and X-11 for the wheels, and a combination if grays, a dark, medium and a light one, don't know which ones would be best, your choice, to give the gravel a textured feel.
Keep asking questions mate, there's always someone here with an answer, or at least a point in the right direction. It's not called the friendly forum for nowt.:thumbsup:
Good luck with your build, and show us some pictures when you're done.
ATB
Tony.