Beltran, to only one of your point above:

no, this is not the case. USCIS dont worry about your past total income...they just look for the offered amount which the company has promised to give him after being permanent resident. THERE IS NOTHING TO DO WITH THE PAST INCOME AMOUNT, but you still have to submit last three years tax return. the only thing they look for is the offer letter by the company.....the offered salary should be greater or equal to the DOL limit. even if you are currently working in the company, they are going to announce the vacancy for your position (for your labor certification - 1 st step, Perm Process", and give you a offer letter "presuming you are the best among all applicant". then, once you get your labor approved,,,they file your I 140- petition for immigration, i believe.  with the approved labor cert and I140 you file I485, which is adjustment of status as a permanent residence. SO, when you apply for I-485 you are going to need all your tax return paper for the last 3-years or whatever you have till now...just for your IRS record,,,but they dont worry about the amount youve earned..........THEY JUST LOOK AT YOUR  JOB OFFERED LETTER THAT THE COMPANY HAS GIVEN YOU DURING YOUR LABOR CERTIFICATION. Thats it.