This recipe is going to produce a somewhat sweet, but very high alcohol (probably 17-18% ABV at least) batch that will be rather hot and harsh and which will need some long aging to smooth out. Is that your goal?
You do not need to boil the honey an water. There are no organisms that will live in honey that is properly cured, so pasteurizing it is simply a waste of time and electricity (or gas), and could give you a scalding. You can just mix the honey in water and it will be fine.
If you double the recipe, you would want to double the nutrient so that the concentration will be high enough for the yeast to grow as much as possible. One packet of yeast is plenty for two gallons, even at this strength. I would increase the pectic enzyme, though it may not make a big difference. As for the acid, I prefer to add it based on taste once the fermentation is finished and it may need more or less depending on personal preference. If you want to follow the recipe, then you double the acid.
You don't need to use orange juice to make a starter. Just rehydrate the yeast properly and you'll be fine. Of course, making a starter doesn't hurt anything.
Rack it when it is finished and the gravity is no longer dropping. Do use a hydrometer so that you can know when this batch is fully done.