You are better off exchanging at blue rate here in Argentina. They accept them at the AFEX currency exchange at the airport but the exchange rate is pretty bad.
I do not use my non-Argentinian cards inside Argentina at all. You lose too much money if you use them. For example based on today's exchange rate a purchase worth 1000 pesos with your non-Argentinean debit or credit would cost you about 107 dollars. With money received via Ria it would cost you...
Only drove it little bit south of Puerto Montt so really no experience, but most of it should be gravel. Also check out the map https://commons.wikimedia.org/wiki/File:Carretera_Austral.png
With a small (regular?) car that route might not be too much fun ... seems more something for suv...
You could drive the Carretera Austral on the the Chilean side. But it is not a continuos road - so you would have to take ferries as well to get all the way to Puerto Montt. https://en.wikipedia.org/wiki/Carretera_Austral
Futaleufu should be the next one for cars that is further south - but I have never taken that one. http://www.pasosfronterizos.gov.cl/cf_futaleufu.html
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By car? Boat? Hiking? Where in Chile do you want to go? I have driven across the Cardenal Samoré between Bariloche and Osorno several times. All asphalt. Easy to drive. You can easily get to Puerto Varas, Puerto Montt etc. or further north from there.