Good Lord I love having Star Wars debates, it almost never happens

1: I'd have to check my source book, but I believe it only took a single one of the Vong's gravity manipulators (though a larger-than-normal one) to bring down a moon. The Death Star might be able to resist a few of them, but it's rate of acceleration was abysmal compared to other Star Wars craft. Put enough gravity manipulators on it and not only would it fall, but they might even be able to keep it pointed away from the planet in question.
2: I can't recall in any instance in the series of the Death Star's main weapon being used on a gas giant. Would the Death Star be able to prevent itself from being destroyed by one of those? Upscaling further, there's no chance in hell of the beam having any effect on a star.
3: Big ships have a bad time with asteroid fields. I recall a moment in Episode V where the bridge of a Star Destroyer takes a direct hit from a space rock, and the ship's captain's image disappears from the conference in the next scene. Clearly something bad happened there.