Once again, I second everything VidaNaPraia has said.

The Amazon is an amazing place, but your vision of the Amazon/Anaconda type is not really within a stone's throw from MAO. The Amazon river itself is so wide, you almost just have the impression that you're navigating in a sea. The trademark experience is when you are either on a kayak or narrowboat down a small tributary, or a flooded section of the rainforest. Because most of the rainforest within the immediate proximity of MAO has been turned into pastures, so you are looking at a 2h drive, and 30 min boat ride from MAO (or 2h boat ride). Ditto for indian villages: the indians have been pushed far, far away from MAO itself. From the lodge where I stayed, it was a 2.5hr ride to an indian village...

You can have the same boat down the rainforest experience in IGU (Argentinean side), and probably even find some indian village (plenty of Guarany living around there). Definitely allocate at least 2, but ideally 3 nights in IGU, but stay on the Arg side which is much more charming, as the Brazilian side is a sprawling, ugly, expensive mess. What I did the last time I went was to arrange the B&B on the Arg side to pick arrange for us a a pick-up from IGU, go straight to the Brazilian side of the falls (where you get a more general view), while the driver waited a couple of hours with our luggage, then off to Arg to relax. And then spend a full day on the Arg side. Day 3 can be spent visiting the park again as you get a 50% discount on admission for the second day. You can also visit the Itaipu dam on the Brazilian side (second-biggest dam in the world).

As for the favela tours, these pics show you what the tour booth looks like outside Santa Marta. It's just on the main street where the taxi will drop you off. The booth is often unstaffed, but I'm sure if you're hanging around looking lost for a few minutes, someone is bound to turn up and offer to help, and might phone one of the guides to meet you.

http://3.bp.blogspot.com/-5fQJudKI2c...0/P1070194.JPG

http://www.trilhaseaventuras.com.br/...ntaMarta-1.jpg

My wife has done it, and says it's really interesting as it's a local resident who takes you around. Will stop at a couple of popular bars for a snack, etc.