I was in Iguazu and BA last August for a total of 9 days. Iguazu was nice (highs in the low 80s), but BA was cold (highs in the 40s, lows just above freezing), so pack accordingly.

I think you may have trouble hitting all 4 destinations in 12 days, considering their disparate locations, although I think there is Iguazu-Salta service (not sure if Andes still does it, but I think AR does?)

As for BA, be sure to visit Gaucho's shop!