I pretty much disagree with most of the advice below in your situation. Here's why. General rule of thumb is not to mix brands; stay in one brand. If it even exists, a 3 part primer is going to be a brand, so unless you want to lock in now (or ignore sound advice) for what you may do in 10 years, I'd just rattle can it with primer and a close match for color and plan to remove it all when your ready for brand name auto paints.
Epoxy primers are 2 part and easy to work with. Next, while some might apply both epoxy and etch primers (the green stuff), the consensious I've read is one or the other is fine. Both are available in rattle cans, with etch being easier to find. 120 or 80 grit is fine enough to knock down 2 part epoxy primer.
I do agree that you should remove as much rust as possible. I would then apply some phosphoric acid product or Zero Rust to kill any remaining and then onto spray bombs. This should keep it good until you're ready for more. Sand as fine as you like, but I wouldn't start with 400.
If you really want a good color match, take a chip or drive the truck over to your local paint jobber and they can match the color and put some in a rattle can for you. They should also have the epoxy primer in rattle cans too. Good luck. Some of that rust looks pretty bad.
My son owns a body shop. I cannot remember the brand name. But any auto body supply will know what you want. Is called a 3 part primer, you get:
1-Primer
2-Reducer
3- Hardner
This stuff is great, with one or two coats and wet sanding between coats with 400 or 500 grit,you are ready to paint.
It fills the blemishes, pin holes,ect.
If he is doing a complete fender or hood that is down to bare metal, he first sprays a light coat of green stuff, I think its etching primer to stop the rust from forming again. Then in a few minutes he sprays the 3-part primer.
Good luck!
Wayne.
