If you're concerned about safety stay away from Rio, it's probably the most dangerous city in Brazil. There is a lot of crime in Brazil's cities, but depending on the neighborhood you can walk around at night. Used cars can be inexpensive because they have a lot of economy cars there. Get a car, a lot of crime in the cities, especially robberies happen on public transportation like buses. Plus without a car you will not be able to drive out of the city. And if you're not in a city you will definitely need a car.
They have hotels there that are called flats and they are basically furnished apartments. You can rent a 2 bedroom for around 2000-3000 Reais/month in Sao Paulo which is probably the most expensive city. It is easiest to find them with a local real estate agent that specializes in renting flats. Do not rent them from websites that are in English because they will most likely overcharge you. I don't know about other cities, but I would suspect that it's less. $3000 US per person and you should be fine for living and partying all you want.
If you want to be away from the city in a beach area, you can rent furnished condos or houses by the beach. The prices will vary according to how nice they are.
DSL service is available, but it is not good in some places. They also have wireless broadband in Sao Paulo and probably other places as well and it is really good. Expect to pay more for the same bandwidth regardless of connection than the US. However, they do have some good free dialup connections.
The language is Portuguese, but most Brazilians will be able to understand Spanish. So if you speak Spanish fluently you will be fine. You will also be able to pick up Portuguese much faster.