Antonio, I am no expert on any of these matters (especially immigration and visas), but I can offer impressions about living in the USA.

Individual health insurance (such as Blue Cross) is available for $1,500 to $1,800 per year (more if you have dependents). Employers often offer health insurance as a benefit (especially true of larger companies); I pay $20/month for mine.

English classes are often available for free or very little cost at local libraries. These sometimes are geared more for people who need lots of help or for Americans who speak English but can't read, but basically they pair you with a volunteer tutor who can work with you at any level. I volunteered for 10 years and mostly just encouraged conversation about "American" culture, idioms, and slang. My point is that you don't necessarily need to be in a large city to have access to help with English.

About salaries...my friend's brother is making $80,000/yr just a few years after getting a computer science degree. I have no idea if this is common. My understanding is that he is involved in software development for a major financial company (something about preventing fraud). He lives in New Jersey.

Any major city on the northern east coast (DC and north) will have a higher cost of living than average for the US (mainly due to rent). This is especially true of NY and Boston. Within the city of Boston I saw rents of more than $1,000 a month for one bedroom apartments. I know it is possible to get a 2 bedroom apartment (unfurnished) in some towns right outside of Boston (e.g., Everett, but probably not Cambridge) for about $700 a month and split the rent with a roommate. The subway lines connect the closest towns to central Boston and commuter trains are available for towns a bit farther away.

The cost of living is typically much less in the midwest and in the south, but I have no idea how easy it is to get a computer-related job there. In New Orleans, you can rent a studio apartment or one bedroom house (unfurnished) for about $400-$500 in the city and $350 in the suburbs and have access to bus routes if you don't have a car. New Orleans is old by US standards, so the city is not that spread out.

real_megia is right about transportation, most US cities do not offer good public transportation (I would add DC to the list, but I think it is an expensive place to live). In some other cities, you can get a bus if you live within city limits (i.e., not the suburbs), but they often are inconvenient and don't run all night. It seems the newer the city, the more spread out everything is, and more people depend on having a car.

You can get a used car in fair condition for about $2,000 (my friend bought one for $300 and is still driving it 3 years later; he was lucky), but then you have to pay for gas and liability insurance (about $500/yr on an old car?). This is what most people end up doing in cities without good public transportation.

Besides cost of living, there are cultural differences among regions of the US. I grew up in the south, and when I moved to Boston people seemed rude. I eventually learned that they are simply more direct and also less likely to engage in conversation with strangers (maybe a result of being crowded so close together, a way to maintain personal space?). I recently moved back to the south and had to get used to greeting everyone on the street and having conversations with every waitress. Plus, they tend to call you "baby" or "honey" (I even heard one "precious"). These terms are meant to establish a congenial interaction and are in no way sexual. I don't mind this now that I'm used to it, but I think most of my Boston friends would be put off by it.

Two notes about contract labor...you are unlikely to have health insurance provided, and you can end up paying more in taxes (although you can deduct some of your health insurance costs and business expenses) because you pay 15% of your adjusted income (after deductions) to social security (if you are not contract labor, your employer pays 7.5% and you pay 7.5%). This is in addition to income tax.

Oh dear, my posts have a way of rambling on. I hope this helps a little.