How do you rent an apartment or house using an imobiliaria in Brazil?

I am a permanent resident of Brazil and have been living with a friend in Fortaleza, Ceara for about 3 years now. I feel that I am ready to live on my own in a house or apartment. It seems that most places rent using an imobiliaria. I would like to know the following:

1. What documents do I need to present to the imobiliaria?
2. How can I rent an apartment or house WITHOUT asking a friend to be the "fiador?"
3. How much in monthly earnings am I expected to prove when renting an apartment? (I do have a carteira de trabalho job, but I earn more in cash doing side jobs)
4. Is it difficult for a foreign person who is a permanent resident to rent a house or apartment in Brazil (specifically in Fortaleza)?

Thanks!

Vonetta
Maia