How many days do I need in Argentina/BA to see what needs to be seen?
I would say three minimum. But if you got more days go for it, great place and everything is so cheap, including the restaurants, ice cream and trips.
I was there from Wed afternoon through Sunday morning at I saw a lot. I could have stayed another 2-3 days to see more sites outside of the city like Tigre or the zoo that @Ya'alili went to.
Great place! It's in Lujan, a bit more than an hour from BA. And you could always take a boat to Uruguay.