Jorge's opinion of you may be wrong, but it has some value nonetheless. Like I said to you before, it would be interesting to note if your acquaintance is middle class and up or not. I say this because many of the people you will photograph will be hostile to the idea of yet another guy with a camera coming to show how poor people can be. The poor and the not poor form two very distinct worlds in Brazil, and many non-poor never cross into the other side. Many of my friends and family have more prejudice than knowledge of that other world, and it shows when they talk about my photography. Such behavior is not uncommon in the middle and upper classes of Brazil, and it worries me that perhaps your acquaintance is like that. If that is the case, she/he would be as much a stranger as you in whatever setting you may find yourself, and she/he may not be the best indicator of how you will be seen there.
If you haven't already, rent "City of God." Although it portrays a particular slum in Rio, I think it will show the separation between the poor and non-poor well enough, if you keep in mind that that was the 60's and 70's. Everything is much more tense today.
If you decide to go, let me suggest going to the rural areas inland of recife. There you will probably find beautiful towns, beautiful landscapes, and great people. Like I said to you before, there is much less tension in the rural areas than in the urban settings, so please keep that in mind.
Also, keep in mind what I said about NGO's. The type of work you are thinking about is much easier to do if you have UNICEF or something like that backing you up. Of course, you would be working for them, probably for free, but its something to keep in mind.
Anyway, don't be offended at what Jorge said; that is the overall feeling you will encounter down there. Jorge may have put it bluntly, but he has a very good point. To invade someone's life, even if briefly and cordially, is much easier if you somehow share in that person's background. In many cases, I was too much of a stranger for some people, and that is simply because I'm a city boy from Rio. Not sharing the language and culture will complicate your situation a lot.
Please don't discard going to Brazil, either because of what I wrote to you before of because of the conversation we are having now. But it may be worth it to go with a different goal in mind. Keep an open mind, I guess.
take care, man.