1

It could be Corrientes city or Gualeguaychu in Entre Rios province.

2

Gualeguaychu apparently celebrates carnaval every Saturday during February so you don't necessarily need to be there on the 11th/12th.

3

La Quiaca, Humahuaca, Uquia, Maimara, Tilcara, Purmamarca. It is incredibly colorful, it has a religious signification. El Tio is the God of the mining, the under world. The most important is Saturday afternoon, I saw one year the starting ceremony in the hill with a monument above Humahuaca main square, music, dance, very colorful clothes representing devils. After they went to the main square to dance with the people there, and I went to Uquia. There is also a starting ceremony, with the devils even more colorful and scenic than in Humahuaca, dancing to the square from a mountain.

Another very interesting place is Amaicha del Valle, south of Salta. It is Fiesta Nacional de la Pachamama. There the tradition is from the Calchaquies indians, the sing "coplas" to Pachamama, Mother Earth in Inca traditions. After one or two hours of coplas, the Gaucho traditons start, with more music and dance. It is every Carnival night during Carnival week. At daytime you can see and participate in popular dancing on the street, see parades, beauty contest for the most beautiful girl with pure Calchaqui blood. Also an old woman with pure Calchaqui blood is choosen the Pachamama until next year.

All over the Argentinian northwest Andes region there are Carnival celebrations, look for more information, I went there many times from Brazil.

4

Will be in Cordoba on the saturday and sunday. Looks like our best bet is Corrientes as the location is a little more convenient than the others i think. Appreciate the advice from everyone

5

Gualeguaychu is your best bet, check out this article explaining the best places.
http://www.spanishschoolsblog.com/spanish-blog/2013/02/06/carnival-in-peru-and-argentina/