I can't comment on all of your questions but here's what I have to add:
The US training route will be fairly affordable compared to others but I don't know what the SA costs are. The costs are slowly creeping up in the US and some might say that it's not always the best option.
I vote for the greencard route, that's what I did and it will give you more employment options in the future.
I would strongly suggest looking carefully into what this industry has to offer.
Do not go into massive debt trying to fulfill your dream, you will be very dissapointed, take it slow and pay as you go if you can.
It's good that you are thinking about work all over the world as opposed to one location.
Get you instructors license in order to help you get that first job and build time.
Most of all good luck and have fun along the way.