It does not sound like you know much about paint and body,its not as simple as people are making it out to be.
If you only have paint scratches then you can sand them out with 180 and key(key means creating a grip for the paint) the whole surface.Then give four coats of primer and key with 600 for the finish.
But if you have deep scratches that touch the alloy there is no way your gonna fill them with paint,you will need body filler for those.