Thanks, man!
I use basic textures or photos (like painted metal, wheels, etc.). Then I do a UV unwrap and export the UV layout to a graphics app (I use GIMP and Aseprite) and paint the textures there.
The headlights are just a photo that I paint onto the model in Blender using Stencil mode (it works best when the image has transparency).
You can find a lot of tutorials like this on YouTube.
P.S. This is the UV layout I made in Blender and then painted over.















