Buenos Aires will be hot and humid during the summer but it will not make you less happy.
There are loads of things to do here in Buenos Aires and in the whereabouts. And Avrooster is right you can actually take weekend scapes and party all you want without feeling any guilt since you'll be always practizing your spanish! Get friendly with the Palermo bars and discos, San Telmo is up during the week and on weekends, Las Cañitas and Recoleta. Some discos may be closed in January but not all. Take a look at Patagonia: Bariloche, Calafate, Esquel, Trevelin, Villa La Angostura, Ushuaia... they are especially beautiful in the summer. I you decide to go to Iguazu or Salta beware of the Very high temperatures and take a very strong and reliable sun screen cream. or you'll return skinless.
You should consider going to the costal spots on weekends: Mar del Plata, Pinamar, Cariló, San Clemente, Mar de las Pampas, Villa Gesel, Santa Clara, Miramar. They are only a couple of hours away from Buenos Aires and are crowded with young people in the summer, you'll surely have fun there and meet people. The beaches are average compared to other famous beaches (there is no comparison possible with Brazil or Caribbean beaches) but they are nice and the cities have their own charm each.
The Lonely Planet guide or the Fodors are the best for students and back packers. You can also get info at the tourism cabins the city "turismo de la ciudad" or something like that. There is one in Florida street and one at the airport.