I'm originally from Brazil and still travel a lot there.
Recife is a beautiful beach city. Like any other large city in the world, it has safe and less safe areas. This should not limit your visit there, particularly because you are going with local people.
For photography, I would recommend MF only. The city is very hot and crowded. It is not easy to move around with big equipment in a hot and humid climate. MF also shows less and people get less intimidated.
For photo essay I suggest the near by city of Olinda and local markets. There you can see a lot historical places, tradition, culture and enjoy good and fresh food.
Bring a lot of film. The supply there is limited and expensive. For speed 100 and 400 will be fine.
Pls let me know if I can be of futher help.