Also mexican. Not sure what visa you are trying to get. But if you just want to work in USA it is very easy to get a visa if you are Mexican and you have a relevant degree. Look at TN Visa. You just need an offer letter. 3 close friends have done that and the process was very simple.
Not that easy. There are a limited quantity each year and the process is excruciatingly long. I was sponsored, had a company-sponsored lawyer helping me and I was rejected still.
There is no limited quantity. The process is very simple, basically you show the offer letter to the officer, answer some questions, prove you have a degree and you are done, no need for lawyer.