ones such as Shopping D and Interlagos -> continue the trend, and make new ones incorporate residential and commercial areas - so rich people could live, work and shop in the same block, avoiding traffic altogether
Soccer is the popular entertainment of choice, but the largest fan clubs ("torcidas") are quite violent -> they could become true gangs, battling an urban war whenever their teams play: Gavioes da Fiel (the Hawks, black-and-white, numerous and violent) roots for Corinthians, Independente (independents, red-black-and-white, sophisticated sycophants) roots for São Paulo Futebol Clube, Mancha Verde (green spot, green-and-white italian brawlers) roots for Palmeiras. Their stadiums are Itaquera, Morumbi and Parque Antarctica, respectively.
São Paulo had a large prison smack in the middle of the city, called Carandiru -> make it return, a mega-prison withbuildings do have AC, though
recreation happens mostly in Parque do Ibirapuera, one of the few green places in the city, open to everyone -> make SP heavily polluted, no green, and close Ibirapuera to rich people only
the outskirts of São Paulo offer nice settings too; from forested sierras that drop down to the beach cities of Santos and Guarujá, mountains waterfalls and an English Village of Paranapiacaba at the South side, to the Cantareira forest and Jaraguá peak that overlooks the entire city in the north side, and actual native-Brazilian villages and reservations in some spots, it's all a 60-min drive away (without traffic)

Yes, the city could sustain a large campaign just by itself... But here's a few ideas for other cities:

Rio could become a decadent urban warzone