One element of the question that hasn't yet been answered: "Is it really necessary to stock 3 types of flour in my pantry...?"
Probably not. At least two are good, but it will cost you more than just buying AP. You can actually blend your own all-purpose flour by mixing a soft flour (like cake or pastry flour) and a hard flour (like bread or "high-gluten" ...
White peppercorns are used purely for aesthetic reasons- just to avoid black specs in a pale dish.
Unfortunately, in my opinion, white peppercorns taste absolutely terrible. They have a sour, astringent, flavor not at all similar to black peppercorns.
I don't think black pepper looks objectionable so I always use it.
You could probably get away without having white peppercorns. There is a slight difference in flavor, but the reasons for white over black pepper tend to be more aesthetic. Just use a little less in black pepper than what the recipe calls for in white. I doubt you'll notice any difference.
I think it is worth mentioning that in the Central-to-Eastern Europe and in other places likely as well, you differentiate 3 basic types of flour according to how fine it is milled:
00 flour or smooth flour, used into sauces;
half-whole flour, for general purposes, especially into most baked cakes;
whole flour, for making breads and dumplings; it is as well ...