Body Work Tutorial

Just started prepping a car for a friend. Its a 73 Duster, original paint from the west coast. The hood roof and trunk lid are surfaces rust so they will be stripped and treated. The side the paint is in good shape but its thing enough that 80grit is going right through it. The primers are a bit tougher. Should I just strip the entire car to bare metal or would it be better to leave as much of the factory primer as possible ?

The primer we have is a DTM high build 2K