Immigration attorney and fees

There is an entire gambit of papers for immigration, not just the I-140. You will need an attotney for the entire process, not just that one document. I suggest that you sit down with the attorney and have them go over all fees and what is expected from you. Or via phone or e-mail if overseas.

It is huge stack of documents that need to be submitted.

The other issue is that right now, only the I-140 can be submitted, nothing more if you are in the US right now. This will not give you the permission to stay or work until there are more visas available.