you can't get a CPL based on a Private Pilot license, even if you have a Brazilian CPL. I use to train Brazilian pilots in the US, if you have a PP, the FSDO will give you a temporary permit with Private pilot VFR privileges (it will have some limitations, most likely no night flights solo), the permit will be valid for 6 months or the duration of the training, as soon as you do your first ck ride, either Multi Engine Private or Instrument you will get the FAA private pilot license (with one of the two ratings on it), as far as flight time you have to meet the FAA requirements for either part 141 or 61 of that specific rating you are going to take first, unless you flew a lot outside flight school in Brazil you will not meet the solo, night and x-country time, if you do the conversion part 141 you will have to do the entire training, part 61 when you are ready you take the test. Standards are a lot higher then in Brazil, you will have to work hard to pass. After you get your multi-instrument or just instrument you can get the CPL SE or ME, for part 61 you need 250 hours for part 141 depends on the flight school, in most cases 50 less. The medical you can get it in Brazil, there are FAA doctors in most big cities.
To get a primary rating in the US, you need a TSA clearance (after 9/11 bs), it will take you some time to get, and before you get finger printed and approved you want be able to start flying.
The written portion, for part 141 as a min of ground school hours you have to take, for ME, Instrument and CPL it's abut two months of class, part 61 you do it with the CFI and it's faster....
How much TT you have? solo? PIC? night? X-country (more then 50NM)? then I can tell you how much the flying portion will take you.
If you just want a FAA PPL, not a CPL, unless you take the written test, the oral and the flight, based on a Brazilian license you can only get a temporary license, and in most cases they won't give it to you unless you go to the US for training.