14 hours is long enough to go to SP
and back to the airport.
Traffic will depend mostly on the time you arrive. The worst traffic during the week are between 07:00 and 10:00 and from 17:00 and 20:00. Out of these times and on weekends, you can plan to get to/from GRU
in 40-50 min.
You don't need to take the expensive taxis to/from the airport. Since you're alone, take the Airport Bus Service to the hotels in Paulista Avenue. They cost R$ 35 (US$ 17) each way and depart almost every hour (see link below).
Paulista avenue is the financial center of the city, and offers restaurants, malls and the Museum of Art of Sao Paulo (MASP
). From there, you can go to Edificio Itália, in the old dowtown, from the top of which you'll have a nice view of many parts of the city.
There are many companies which sell guided city tours, such as this one (just an example, I never used it):
If you like to eat, Sao Paulo is THE place to go. There are several wonderful churrascarias in the city, among them:
Fogo de Chão:
Baby Beef Rubaiyat (at Alameda Santos, 85, near Av. Paulista)
In these places, there's not only meat, but the price includes large buffets of salads and seafood. These churrascarias are not cheap, though. Expect to pay around US$50 (buffet + steaks).
When going back to the airport, leave 3-4 hours before your schedule departure time, and avoid rush hours if possible.
Crime: while Sao Paulo is definitely not a safe city, you'll probably have no problem to walk around alone near Av Paulista and the neighborhoods immediately south of it. Make sure you don't walk around showing off your Rolex nor your fancy camera. Sao Paulo is the most cosmopolitan city of Brazil, and you'll not feel like a tourist.
I suggest you to post your question in travel forums, such as TripAdvisor or Lonely Planet, where you'll probably get more answers.
Have fun, and if you need more specific info, pvt me!