Wow - controversial topic. Better ask your painter what he will accept.
I would use epoxy primer.
I am NOT an Automotive Painter but???
I have sprayed all kind all materials (airless, HVLP, airbrush) & if You start the paint prep then expect to pay 2x the cost for them to "fix" your work if you expect a good quality job & any form of warranty.
Just strip off the body parts & if you have bare metal lightly spot prime with something for protection & otherwise leave it alone.
I prepped my car when I was bored back in about 96-97 but I own a painting company & they still didn't accept some areas that I worked on & presented as paint ready. I only paid $600 for the spray work but it's far from being a Great finish! I don't care that it's not perfect & it still looks decent but be careful before you end up costing yourself wasted time & extra $$$ for the finished product.
If you are serious then look up some automotive painting forums (they must exist) & try to learn some basics & make a plan before you just start sanding.
You can do some of the prep but do your research & remember it's really Dirty Work when that paint dust gets on everything you own & in your eyes, ears etc.
