Do you have water spots on the car? If not then no need to use MDR.
Keep it simple and this is what I would do
1. Ferrex. If the paint is not that dirty you can use that over the dry surface to not dilute the product with water. If it is too dirty wash and dry first then use Ferrex.
2. Rinse the Ferrex from the surface and proceed with your normal wash
4. Paint prep if you want to take an additional step after claying to remove any clay lube residue. No need for an additional wash.