When you can scratchbuild at your level, why even bother with kits
Great pair of projects, I agree that the Renault truck cab is of a most excellently ugly design.
When finished you have plenty of choices for service and paint scheme for the Renault. In a book I recently read it advised that french auto manufacturers (Citroen, Matford, Peugeot & Renault) produced well in excess of 50,000 trucks for the Wehrmacht.
Are you going to build any of the underframe detail on the rail wagon ? Its mostly not seen. I see in the plans in your pictures that these wagons seem to have a triple valve & air reservoir (air brake equipment), I have some of these in 1/87 scale, a bit small but placed underneath the wagon the thing is barely visible, only partly seen even at ground level. Even if a bit small my spares may be a good basis for modification. The type I have are not german types from the 1930s but they are all very similar.