A body kit should be fine unless it's hanging on. The wing probably can't be any wider than the car itself. Paint shouldn't matter, nor should decals. The legality of suspension only comes in with a drop, so that I'd say to check on. Swaps won't be a problem, since there are only 3 practical engine that can go on your car, the one that came with it, its counterpart, and the 3S-GTE (assuming your car didn't somehow come with it).