What primer will you be using?
Based on the manufacturer's recommendations, no primer. To that add that I have used Rustoleum (I actually used to work at the Canadian plant that made this stuff) rust paint before without primer and achieved good results. To that add that most of the original paint is going to be painted over. The original paint is hard and stuck like poo poo to a blanket. So, no primer this time - fingers crossed. That said, something has given me cause for concern...
Are the decals I ordered from Velocals decals or stickers? If decals, time to rethink the paint plan.