Travel insurance is no longer mandatory and TIMATIC/TravelDoc have been updated : problem solved !
https://www.flyertalk.com/forum/32725003-post17.html
I highly encourage you to have a proper coverage when travelling to Brazil though, because medical expenses can be huge there.
Regarding Sao Paulo to Rio de Janeiro, I would not bother driving or sitting on a bus for 6 hours when you can take a 45 minutes domestic flight departing from both city centers (yes, CGH and SDU airport are very well located). It's very cheap if booked in advance (less than 30 USD). Check the brazilian website of the domestic airline you want to use (Gol, Latam, Azul) or book through expedia.com.br because in my experience it was cheaper.
As a foreigner, I would never bother or take the risk to drive in Brazil without speaking Portuguese and without a good knowledge of the places you are going (you might end up in dangerous places even with a GPS).
Use Uber, the metro, and domestic flights, it's the best advice I can give you. They are reliable and good ways to get around safely in Brazil. Also, Uber is super cheap. 15 minutes ride for something like 3USD due to the fall of the BRL, so really, don't bother renting a car...