I would say that they would probably mirror the other monetary systems, and any war as an impact on the economy of the countries involved. In America, wars have been good for the economy. (if you don't count the current mess, which clearly is the exception). And I would think yes, being involved in a 'civil war' of sorts would certainly affect the economy.

I think the Goblins would charge interest. And I would absolutely believe that they would be invested internationally. They're too clever not to.