Don't mean to pull an MC here, but forgot something:

You will need a passport, of course, but not a visa. Be prepared to
pay $100 U.S. when you enter the country. The nearest fair size town
to Patagonia is Coyhaique right at the foot of the Andes, and near
lots of rivers. You should be able rent a car/truck there, and there
are hotels available. You will probably fly into Balmaceda which is
serviced by jets out of Santiago de Chile.

Good luck in you plans.

Dave