Take the scratches out with 240-300ish grade, depending on severity, then move onto 400, then 600 grade, flatting it off until it's really smooth. Use plenty of water and a drop of washing up liquid also helps.
You'll need to apply at least 3 coats of colour to get it looking good. Are you using lacquer separately or is it in the paint?
Have you asked anyone in the vehicle refinish trade if they would do it for you? Metallics can be awkward to work with if you're inexperienced but a car painter would have no problem.