Painting question - rattle can stuff

[hillcountryflt]

I am clearing out my cab - seat, fuel tank, heater box, rear glass, headliner, firewall cover, Leaving windshield (will tape up) and side glasses. Pulling rear glass as the seal is breaking up anyway.
There is some surface rust in areas. Others not.
I don't have a paint booth or spray system, so will be rattle canning it with some spray paint mixed by English Color (I provide the paint code - Boxwood green in this case).
Is there one primer I could use for the whole cab? Or do I treat rusty areas with ospho or por15 and then paint (or prime). I will not be bringing it to bare metal. So any primer would have to be good for use over existing paint and bare metal as well, which is why I was thinking of using etching primer.
Painting will be done with single stage enamel.

[Ranchero50]

These are question your paint guy should be able to answer. To me, remove as much rust as possible however necessary. You'll also want to spend a lot of time removing any oils. Acetone on a old white cotton shirt does a pretty good job of showing where you need more work. Of course, spend more time on the areas that show once assembled.

[farmallmta]

Sounds like he IS his paint guy. Thus the questions.

Here's what I do in your circumstance: Wire wheel in the side grinder to brush away nearly all loose paint and rust and dirt. Clean up with a non-water cleaner like Wipe-Out. Then Ospho for heavy rust, or Rustoleum's spray on rust converter in flat black for minor rust-ish metal. Then a heavier primer to smooth the surface out, applied liberally. A sealer primer in a color near your own (black, grey, red, white are readily available sealer primer colors), smooth out with minor sanding if you like, then on to your finish paint.

One hint for you on rattlecan paint jobs: use two cans, one in each hand, at the same time to get enough material on to get the flow-out you're looking for. This way you keep moving fast enough to stay near-- but not go over-- that ideal flows-but-doesn't-sag sweet spot you need for a good finish with minimal orange peeling. The trick on the two-can technique is you're holding the cans fairly near one another, both are supporting the other in your hands, thumbs touching one another. Try this on some other flat surface first. Once you get the hang of it, you can do almost as well with two rattle cans working together as you might with a HVLP gun. Much better results than with a single can.