Corroding paint, nasty paint on A-5

Hey everyone... to make a long story short, I used to have a Tippmann A-5 with E-Grip, Boomy, and some other nice upgrades.  The gun served me very well but I ended up getting an E2 Autococker (see marker pics page).  I sold the A-5 for 400$ which was a great deal for me but the kid I sold it to lost interest in the sport and proceeded to give it to my friend who misused it and treated the A-5 like crap, tearing it apart, and never cleaning, maintaining, or fixing the gun.

I finally retrieved it from that friend who doesn't need it as he has an Ego and Intimidator so I went about starting to reassemble it and clean it today.  First things first, there is nasty old paint that is acting like a corrosive adhesive all over the gun, it caused me to use Goo Gone inside the barrel to remove the old paint, and it has nearly dyed the body of the A-5.  The matte black paint coat on the A-5 is also peeling away and the metal underneath is rusting.  What would you guys suggest I do?  I would like to sand it down and repaint it but what type of paint should I use and how else should I go about getting this gun back to normal?

Pics? Also, did you get it back for free? I would just steel wool it and then use duracoat.