It's an interesting one with the ANH helmet as in order to be truly movie accurate, the gun metal grey at least would have to be hand painted.
But - for a better quality finish a professional auto shop is a great idea as they have the right tools to achieve a perfect finish.
Colours would be Gloss Black and Gunmetal Grey - I have used a few different shades of gunmetal, lighter and darker shades. The auto shop should have some colour charts for you to choose from, I think.