In order to visit São Paulo you will need a couple of days. If you have more time, you can visit some of its excellent museums in detail, or even better, take your swimming costume, go to the Jabaquara Metro Station, and take one of the buses to the excellent beaches in the region.
The nearest beaches are Santos, São Vicente and Praia Grande. The most beautiful towns are Santos and Sao Vicente. In the coastal towns you will find restaurants, bars and hotels. A good idea is to rent a bike to visit the beaches. These cities are relatively small.