-Sure cure is correct, technically it would be .48 oz but 1/2 is perfectly fine!
-2.88 for the sure gel but again, 3 is fine
-This is where we get into personal preference a little, 2 quarts of water per 25 lb batch will be fine but you can get away with less, which will “change” the consistency and will certainly speed up your cooking process. If you want to use a full quart for 12 lb that is fine but you might have an easier time if you use about 25 oz
For Willies 2.5 cups is a little too much. ½ cup, 4 tbsp and 1 tsp is enough for 5 lb so it would work out to just about 2 cups, slightly less I think but very close. I would also recommend you do it by weight rather than volume. That weight would be almost 13 oz.
Good luck!