Sanding grits on bare metal before primer and after

[88Stanger]

Ok, so I am by no means anything close to a body guy but I have a very basic knowledge and like to lwarn, so with that said I have done all the rust repair and such and now I getting ready for 1st coat of primer/sealer. To start off I had the truck sand blasted so I am working with metal. I have repaired all the holes and rust areas and now I am getting it ready for the high bond primer/sealer.

1.) My question is what grit sandpaper to use on the bare metal areas before spraying the primer/sealer?

2.) After I get the primer on I will be using Dry Guide coat and looking for issues, use a cream filler as needed and then for final sanding what grit of paper do you use? I will be applying a single stage urethane Satin Red