I think you're trying to do too much in eight days. I would totally skip the car in Brazil. Depending on your interests, it might not be enough time at the falls, especially if you stay in the park to enable you to have early morning and late afternoon/evening access away from the crowds and to see sunrise and sunset at the falls. [There's also a huge dam and electric power plant that I wish I had been able to see.]

If you're committed to flying into EZE and out from GRU, you might want to skip either Rio or the Falls. Otherwise, I'd consider skipping SP.