For light scratches you could use Brasso or some other rubbing compound and model wax like The Treatment or others like Macgiure"s or Mother"s. For heavier scratches you'll need to sand and polish. I start with 1200 grit sand paper and work up to 2000 grit. Then I polish using the above.
The decals are an easy one. Toss them! Academy/Minicraft are notorious for this problem. You didn't say if you gloss-coated before applying the decals but in the future use Future to build up a somewhat glossy surface to apply the decals to. Then use your solvent. The repacement decals willstick better and there won't be any silvering.
Search the forum for the compete technique. Hope this helps. Oh, and BTW,
to the forum.