The Kalahari is brilliant - and easy to visit.
Even for an area I know well, I prepare a shooting list of subjects I need.
A large wildlife book, start to finish, could take one to two years, but then I would expect to get several good (nature) magazine features off the back of this, plus of course a lot of stock.
In The States I would have no edge, no advantage at all.
I would never dream, for example, of going to The States to photograph your wildlife.
I also like flyfishing - maybe I would have figured a way to make a living out of that?