As someone who has undergone the tormentuous path of U.S. immigration, H1-B and green card processes and who is currently living in the U.S., with respect to the economic prospects of this country, my advice is that IT IS NOT WORTH IT. I think Brazil has a better economic future than the U.S.
If the above was not enough to convince you, let me tell you that the path of H1-B is the gautlet of indentured servitude. I started the process once in 2000, got laid off from that job the following year, started all over with the next company, didn't like the job, quit it in 2003, started all over, stayed with the next consulting agency through a series of unhappy work assignments just to get the stoopid green card. It was a path of misery, waiting, and humiliation. America, for all it has to offer, is not worth it. I have damaged my health and my life in the process. But I am living here now because 1. I do not like living in my home country and 2. I do not want to go through the immigration process again somewhere else. There are many countries where I would rather live if they readily handed me their permanent residence (Brazil included).
What are the knowledge, skills and abilities that would be expected from a foreigner candidate in the field in these countries?
What are the documents and other process I should be looking up to?
Let's say that didn't convince you either and your are still determined to come to the U.S. Personally, my advice would be to get a tourist visa, come here for 2 months and look for a job that will sponsor you fro H1-B. In the process, I would also intensively socialize and try to meet a nice girl who might want to marry you, I am saying "nice" because there are all kinds of predators out there who will hold you hostage and demand all kinds of ridiculous counterfavors.
As far as hard skills independent of immigration logistics, I don't think they are much different than what is necessary to survive in Brazil. If you are a good programmer there, you will be a good programmer here. My experience with most Brazilians is that they all transition into English fluency fast as the language structure is similar. I know Chinese people who can barely fumble a sentence, yet they are top programmers and they make it just fine. So I wouldn't worry about it.
The biggest obstacle, like I said, will be the immigration bureaucracy.