The Isshu region could be still a part of Asia, I don't know if they would really take a part of the U.S like N.Y.C, and make the region or city resemble it, there could be other cities out there that could resemble the region in some way.
I actually think that they might add at the most 150-200, I would love a variety of unique looking Pokemon. If I see too many machine looking Pokemon used, it wouldn't be interesting at all..
I too don't use a masterball, one reason why is that I caught an Entei with a pokeball, and I assume that that could happen with any other Pokemon. Patience is the key.