Welcome to Flyertalk.

Since you are going Manaus to GRU, you are domestic. As such, you go through passport control to enter the international departure area. Usually there are a number of flights to the US departing in the late evening, so I would expect things to be a bit busy. That said, for a 5 hour layover, there isn't a lot to do once in the International departure area except use one of the clubs if eligible. If your flights are on time, I would say you would be OK with a 2 hour visit to your friend's hotel. On your second topic, can't help you much.