VMA's aren't what they used to be but still a lot of fun. Make sure you figure out where the after parties are. Dress is "rock star semi formal" -- which basically means try not to look like a dirtbag and don't look like a banker either. Basically go on Youtube and look at the red carpet arrivals for the Grammys or VMAs and you'll figure it out pretty quick. Depends on how much of a rock star you look like but something like a blazer and jeans or similar for guys is pretty typical if you're not a rock star. Don't wear a tux or a suit with a tie. Unless of course your suit makes you look like a member of Green Day. You get the idea.

Street closures and similar shouldn't be a huge issue. You can certainly take a taxi there, though Radio City is directly above the Rock Center subway which I can't imagine will be closed.