They have recently started online service as well.
So, I think you should receive documents by both mail and will be made available online for download in your USCIS account.
The time given for track one is average time to process request.
You should get your documents more or less around that average time.
Create an account on USCIS website and link it to your case, you will be able to log in to the digital delivery center to view and download the records you requested.
Already have a USCIS account? Simply login and link the case to your existing account. USCIS will email you when they have processed your case and your records are ready to be accessed.
No, you can’t upgrade i140 to premium yourself.
Your employer has to request it.
You can pay your employer and then they can upgrade it.
If they are not upgrading it, then it means that they want to keep you stuck with them as long they can
i140 A number generation
A number can be generated at the time of entring your data in USCIS system too. Approval is not necessarily required.