there are a bunch of great painting walkthroughs on here... look for the ones by spideyfett and r_boba_fett - both are great.
i did the silver first, then layer the colors on method. i used liquid mask from an art supply store to mask off the areas that i wanted to stay silver, since the idea of using mustard just bothered me.
for scratching, i used a caligraphy pen and a nail.
but yeah, if you read back through some of the old threads on the subject, you'll find all sorts of good stuff, and lots of pictures.