Asylee13,
My reason is family related emergency. I included evidence of the urgency to support my request for expedite service.
I think it is important that you include evidence and reason, otherwise, anyone can submit a request to expedite. If you do not include support, with good reason, they might ignore your case... just an opinion.
It is "my opinion" that you will need to have your fingerprints retaken, for one, you paid the biometric fee and they take different prints for different applications, secondly you need to have your photo taken, i think that is a check for them. I would look at the I-485 as a separate application all together.
yes! express mailers are found the the post office. They look like the flatrate envelops except that they have a stamp in the amount of approximately $17.
I hope I have answered your questions. Oh wait, I received a two letters separately, the receipt notice, with the directions on what the next steps would be- a mere formality on their part, and second Appointment notice (inside one of the express mailers) all within a week of mailing in application. Will keep you posted.