Well for the silver, you do not want to use spraypaint. While your at Micheal's picking up the snaps I showed you, you'd want to get some, "Silver Leaf" Rub 'n Buff. Just rub it on, buff it shiney, it's what the Jango Fetts use to make their suits look like pure metal, and it turns out fantastic.
What would you mean by weathering the silver? I'm guessing that the suit is silver with the yellow trim. In order to make it look a little beaten up, or just plain dirty, I'd recommend that you buy some black, brown, aubrun acrylic paints, and make a black wash. A black wash is where you take the acrylic paints, mix it with some windex (20% paint, 80% Windex) and you softly sponge it on several times. You could even take some flat black spraypaint and give it a very light mist.
About the soft goods, airbrushing works beautifully, but don't go overboard.