Hey Marc,
You have made a lot of progress! Good work! Especialy the gasoline staines

This is the trick of modulation style (in a nuttshell);
- gray primer- paint the whole model in grey. This because the outcome of the final colors...
- dark 4-bo green- spray (or paint) this only were the sun don't shines like the undersides and the space where the wheels are and the underside of the turret.
- 4 bo base (genuine color)- spray (or paint) the sides of your model and the wheels too. Don' forget the turret sides and the barrel

- 4 bo light base- spray ( or paint) the upper decks, turret roofs and upside of the barrel...
-4 bo highlight- paint small places like hinges klamps and klasps, some small hatches with a bit lighter color than the light base basecolor.
Than a filter for dark green vehicles.
Happy painting!
Remco