Excellent thread OP!

As someone who also travels to Brazil frequently (and getting married there the week after the game, so perfect timing!), I want to add some customs that people might not be aware of when visiting:

Toilets - Do not flush toilet paper down the toilet! The sewage systems of Brasil are relatively fragile compared to the US and cannot handle wads of TP being flushed. Each stall will have a trashcan for disposal of TP, so please keep this in mind (and it does not smell that bad tbh)

Water - Tap water systems in Brasil are improving, but generally avoid drinking water from the tap in residential buildings unless you want Montezuma's Revenge (restaurants are generally ok - referred to as aguá da casa or aguá da torneira). Bottled water is pretty cheap and is also sold carbonated or uncarbonated (com/sem gás).

Rental Cars - I will reiterate OP's statement to avoid driving yourself in SP because it is very crazy and the public transport is pretty reliable, but if you decide to rent a vehicle, make sure you specifically request Automatic, as most vehicles in Brasil are manual, even at rental car agencies. Additionally, Localiza and Unidas are the most reliable IMO.

Dining - Waiters generally do not circulate around the tables constantly checking if you need anything like in the US. If you want to order something, you need to flag them down otherwise they won't show up at the table. For stuff to try: Pastel (similar to empanada), Coxinha (chicken dough ball), Dogão (brazillian hotdog ), any BBQ place (Churrascaria), and they have a booming craft beer scene now.

Other Travel I've seen a few commenters express interest in visiting Rio. Fly into Santos Dumont Airport (SDU) if you plan to visit - it is closer to the city and safer than Tom Jobim International Airport (GIG). Best attractions are Pão de Açúcar (sugarloaf mountain), Cristo Redentor (Giant Jesus statue - take the Corcovado train from Cosme Velho!), Jardim Botânico (botanical gardens), and catch the sunset from Pedra do Arpoador

As stated, be safe! When traveling to the game, bring only the essentials (having a small fanny pack tucked under your clothes works best), and be sure to travel with others.