GRU just isn't that big of an airport. Getting from one end to the other is easily navigable. The time you have should be more than plenty. Yes, the arrivals area, luggage pickup, can be busy in the a.m. but it moves quickly. Otherwise, GRU is pretty quiet in the morning. The vast majority of its long haul departures don't start leaving until late afternoon through the evening.

As for breakfast options, those are disappointing. There are two pretty good restaurant options at either end of the terminal but, unfortunately, neither is open for bkfst. I think they open at 11 a.m., at the earliest. There are a number of coffee shops, with open seating, where you can grab a pretty good coffee, some snacks, bkfst, etc. There are also a few stores to shop at, but nothing that stands out. There are numerous ATMs and banks for changing money. Have fun.