I agree that taking down to bare metal is best. With all the curved surfaces on dashes, I find it easiest to use wire wheel brushes and a 4" angle grinder to remove the paint, this leaves the metal smooth and not scared as can happen when using 80 grit. Plus it's less caustic than using strippers.
After paint removal the use of either an etching primer, or epoxy primer will ensure good bond of topcoat. I'm obviously in the middle of full paint/body work and plan to use BC/CC body color into the dash, but will be using Black SEM interior paint for all other exposed panels.
I suggest you look for materials at your local auto body store rather than a general parts outlet like pep-boys as they'll have products geared specifically to your application, and will almost always be of higher quality. Good quality rattle can etching primer can be found at the auto body stores. 2 part epoxies need to be mixed and sprayed with a gun.