If you are going to take the car to a paint shop anyway, let them do the final prep and prime/sealer application. Do not use any rattle can spray primer. All the new urethane paint systems are not compatible with lacquer rattle can primer.
I do recommend they seal the car before painting even if the current paint is sanded and looks good. The sealer will limit any solvent in the new paint from transfering to the old paint and causing any reactions.
