Definitely not an exercise in minimalism, this one.
A JCB that is earning its living in a rather muddy environment, getting itself covered in all sorts of muddy substances.
The plan here is to work on one layer at a time, and leave the model at each stage in a state where it could be regarded as finished. This will serve to show (I hope) how to build up layers of dirt gradually until satisfied with the result, whatever stage that might be at.
No airbrush. This will all be done with pigments, Dullcote, one enamel wash and a drop of PVA. Two brushes, a rigger and a filbert. Cotton buds - make-up style rather than baby style. Maybe a tinlet of Revell enamel 84 applied with a microbrush, but let's wait and see if that's practical.