Assuming an arbitrary number of force dic, consider a hypothetical situation-

FFG Starkiller sees a star destroyer. It is too big for him to Move, even with all the sillouette upgrades.

Instead, he starts ripping sillouette 4 hull plates "out of secure mountings" to tear the ship apart.

How would you resolve this? Does the star destroyer get armor against having its armor ripped off? Is there an opposed roll? Opposed by what? And can he use magnitude to select mutiple hull plates at once? Would it be one attack, autofire, or separate rolls?

Well, I would say Hull fused together to prevent breaks in the ship that could suck people into space, and a Hull strong enough to resist even the most powerful lightsaber is too strong to just pull off, even with the force. So I probably wouldn't allow it in the first place.

But for the sake of things, let's say the pieces of hull are impossibly loose, and so the only reason this force user is next to it in the first place is because it's just completely wrecked and it needs to be heavily repaired. So, if his goal is purely to rip the hull off (and not attacking characters), then yes, he can rip off multiple panels at once with as many points/ranks in magnitude as he wants to, no check needed (because in this case, heavily damage hull can be close enough to secure mountings), just needs the force points.

But if you really wanted to allow the player to try yanking it off an intact Star Destroyer, I'd consider that as an "Impossible" check against their Discipline, and should be set at 5 Difficulty at the absolute minimum (this would probably fall in line with the book's suggestions where it makes sense to push the difficulty above 5), require spending a Destiny Point, and maybe like 3 difficulty upgrades? With more than a few Setbacks added as well depending on the situation. And of course, the necessary Force Points. Other than that, no check needed unless they plan on attacking somebody/thing with the hull pieces, in which case you'd move on to another Discipline check using the book's rules and applying normal ranged combat rules (+1 difficulty to auto-fire, 2 advantage for each piece to hit, highest difficulty of intended targets, etc.).

Well... a sil 4 object does 40 damage when thrown... so for sake of argument let's say ripping off a hull plate will do this much damage. AFB, but I'm betting that a star destroyer has more than 4 armor. so I would say it is just outside the purview of the character...

But further thought exercise! Let's say that same character had seek with the upgrade allowing for additional pierce. So 40 damage base, difficulty 4 check (with extra successes granting damage) bonus force points granting damage, and the pierce quality of say...7? so if the damage +pierce could rise up above 50, you might have a chance (maybe not against a true capital ship, but a destroyer or frigate you might EVENTUALLY be able to deal some serious damage to).

Now, that being said if I were to have this come up in a game, I think I would have the player make a daunting to impossible resilience check, based on the speed in which they were trying to do this. Because it's not at that point a question of can they, but more about how exhausting must that bee, even for someone like Starkiller.