I will try to answer your questions in the same order as you asked them.
1) The 0 flour you have is not what we call a high-gluten flour in the U.S. It is an Italian flour that is milled so that it retains about 70% of the grain. Most of the members of the forum who use the Italian flours use what is called 00. It is the most refined of all the Italian flours (followed by 0 in the pecking order) and is used to make Neapolitan style doughs/pizzas. Because the 0 flour has more of the grain, it will be slightly darker and coarser than the 00. Most Italian flours used for pizza doughs have lower protein contents and lower gluten levels than our domestic flours and behave differently. So they can’t be used interchangeably with our domestic flours. You will have to find recipes that best use the different flours, including the 0 flour you have. There are a lot of 00 pizza dough recipes on this forum but none for 0 flour to the best of my knowledge.
2) You will not find high-gluten flour in Whole Foods although many Whole Foods do carry the King Arthur brand of bread flour. Unfortunately, you will not find high-gluten flour, and certainly not the King Arthur Sir Lancelot (KASL) high-gluten flour, at the supermarket retail level anywhere. The gluten flour you saw is what is often called vital wheat gluten (VWG). It is not the same as high-gluten flour. Rather, it is a dried wheat protein of high-gluten, hard wheat grain that has had all of the starch removed and is then dried. It is frequently used to supplement other flours to increase the overall protein level of such flours. For example, you could add VWG to bread flour to increase its protein content to approximate that of high-gluten flour. But, it alone would not be used to make a pizza dough.
3) My preference among high-gluten flours is the KASL flour. But there are many other brands of high-gluten flour that can be used to make NY style doughs. Whether it is worth the price and the hassle to get KASL is a personal decision that one has to make. But since this question comes up time and again on this forum, I would like to suggest that one way to approach the matter of high-gluten flours is as follows: Start with bread flour to make your pizza dough. If you are satisfied, then that ends the matter. If you still aren’t satisfied, you can try adding VWG to the bread flour. (I can tell you how to do this if you choose that route). If you try the VWG/bread flour combination and you like it, then you need not look further. If you don’t like the VWG/bread flour approach, then you can try to find high-gluten flour. Since you won’t find high-gluten flour in the supermarkets, you will have to look for another source. It might be a distributor, a foodservice company, or it might be one of the big box stores like Costco’s. Depending on the source, the high-gluten flour might be KASL, All Trumps, Bouncer, ConAgra, Pendleton, or whatever. They will all work to make a NY style dough. What will usually dictate what you buy will be availability in your area and price. In most cases, however, you will be buying a 25-50 lb. bag of flour. One advantage of the KASL, if it matters to you, is that it is unbleached, and non-bromated. It also has a higher protein content, 14.2%, than just about all competing brands. Whether that matters is again a matter of personal choice.
4) All supermarket packets of yeast weigh 0.6 oz. (7 g.) and contains 2 1/4 teaspoons of yeast, whether active dry yeast (ADY) or instant dry yeast (IDY). What you may be thinking of is the relationship between the use of ADY and IDY. In that case, the answer is that 2 1/4 teaspoons of ADY is equivalent to 1 1/2 teaspoons of IDY.