Sounds like a great trip, South America is wonderful. Like others have said, work on Spanish as much as possible. BsAs is in its own little world. They speak a different kind of Spanish, and the people aren't very patient. That said, it is really cheap. The wine in Argentina is fantastic and cheap even in restaurants, the malbec grape is dominant there. Carmenere is popular in Chile. Both countries produce fantastic wine. Also drink pisco sours while you are there. I spent most of my time in BsAs half drunk and with a belly full of some of the best steaks I've ever had. Get your steak with a fried egg on top, and lots of chimichurri sauce on the side. Also, pizza with hard boiled eggs is pretty good too. I also really enjoyed strawberry juice and mora (blackberry I think) juice in the mornings. Watch for all the little kids begging though, they come right to your table at restaurants and set pens and such there hoping you buy the stuff.
In Colombia, travel low profile, and you'll be fine. In Bogota, the museum of gold is cool. Aguardiente is the hard liquor of choice in Colombia. I found Colombians don't drink that much though. People in Colombia are really friendly. I love it there. The food is fantastic as well. In Bogota, make sure you eat some ajiaco. It is a wonderful soup. Bandeja paisa is also good, but make sure you are really hungry. In Cartegena eat arroz con coco. Drink agua de panela. Arepas are fantastic, but my favorite of all was pan de bono. Colombia also has great steaks, served with yuca, either fried or baked. Best of all was the fruit. If you have a sweet tooth, you'll be in heaven. There are approximately 50 billion different kinds of fruit in Colombia, and they are delicious fresh, made into ice cream, or made into fruit juice. I suggest granadillas and pitayas. Also don't forget Colombian coffee.
It is probably obvious that I travel on my stomach.
Oh, and this so completely obvious, (just look at the top Miss Universe contestants this year) but the women in South America are amazing. Friendly too. Life is good in South America. Enjoy yourself.