That's not how it works; for the dealership to deny a warranty repair, they need reasonable proof that your mod caused the damage. An engine light is a warning light; it does not indicate any damage is done.
Given that the exhaust does not stress the car, it's a safe mod that will not get you...
I don't have any numbers, but the HP gains will be the same as all the other aftermarket intakes, ~15 whp
it sounds louder than stock but not too loud as its a closed intake.