>secrecy about their exchange rates
Fact is they make quite a bit money from these transactions because their exchange rates aren't competitive, at all. I would assume that's why they don't display them openly.
Go with C. Write a few simple programs and compare its performance to other languages. You'll learn to hate everything else. :) On a more practical level, it's good to have a grip of it before trying C++ no doubt.
Go for lower level if you're after deeper understanding, higher level if you're...