The first major goal is to get the mechanicals all sorted out, and rebuilt.
This may also require work on trucks wiring, exhaust system, radiator, etc.
It needs to start... run... steer... stop and so on.
Next might be replacing any glass, hinges, latches, bad sheet metal, and so on to make the basic body functional.
Don't even worry about starting on the bodywork, paint or interior until it is functional and drivable. The reason is that there is th epotential for damaging the pretty new paint and interior, while you are working around it.