For a NY style pizza dough, the flour that is usually recommended is a high-gluten flour, with a typical protein content of around 13-14%. So, there is no need to add any vital wheat gluten (VWG). If you choose to use a lower protein flour and supplement it with VWG to increase its protein content, this can be done with reasonably good results. I did this recently and reported on my results in the Lehmann thread at http://www.pizzamaking.com/yabbse/index.php?board=5;action=display;threadid=576;start=msg5635#msg5635
As for the ascorbic acid (Vitamin C), as you may know, a small amount of it is often added to instant dry yeast (IDY) and, on rare occasions, to active dry yeast (ADY). The ascorbic acid acts as a nutrient for the yeast and speeds up its action while strengthening the dough (by preventing the gluten bonds from breaking down). Sometimes ascorbic acid is also added to flours that can be used for making pizza dough. I use IDY almost exclusively in my dough making, including NY style doughs, and have not found using such yeast affects the final product in any noticeable way. In fact, in a conversation I had recently with a representative of one of the major suppliers of yeast, I was told that the amount of ascorbic acid in IDY is very small and unlikely to materially affect the end product.
With respect to diastatic malt powder, I assume you mean the barley malt form as is commonly used in the bread and bagel making trades. This is barley that has been sprouted, dried and ground into flour, and can be used in place of, or together with, other sweeteners to feed the yeast. The diastatic malt works through enzymatic activity (it provides additional alpha-amylase) to release sugar from the damaged starch molecules of flour (to produce maltose), which aids yeast action during fermentation as the dough rises. This is believed to give the resultant product an improved crumb texture, better flavor and more color (because of the Maillard reactions involving the maltose and any other reducing sugars in the dough). The amount of the diastatic malt to use has to be carefully controlled. Using it in excess can result in a slack, sticky dough and a gummy crumb in the baked crust.
I have read that the three ingredients mentioned above--ascorbic acid, vital wheat gluten and diastatic malt--can be combined to use as an additive in doughs. I believe such products are even available commercially. And sometimes ascorbic acid and barley malt are combined in flour. While such dough enhancers may be useful in preparing yeasted doughs--and especially breads--in a commercial setting, it is not clear how useful they are, or if they are even necessary, to produce good pizza doughs in a home setting. The NY style pizza doughs are made so that the resultant crust is leathery and chewy, rather than fluffy and soft like bread. If a more open, airy crust is desired, this can usually be accomplished by increasing the water content (hydration). The average home pizza maker should be able to make a decent NY style pizza dough by using a good high-gluten flour, IDY or any other form of yeast, relatively high hydration levels (e.g., 58-65%), and sound dough production techniques, preferably including a period of refrigeration.
As a final comment, you are correct in suspecting that a period of refrigeration might produce its own set of effects. The refrigeration, especially if coupled with the use of cool water and little or no added sugar, will slow down all the fermentation processes. Yet they don't stop altogether and the desirable by-products of fermentation will be produced and contribute to the flavor and texture profile of the finished crust.
FYI, for a good discussion on malt, diastatic and non-diastatic, see the Tom Lehmann Q and A excerpt on this topic at http://www.pizzamaking.com/yabbse/index.php?board=7;action=display;threadid=609