In other situations you might have been able to do "interfiling" to transfer the old I-485 onto your marriage-based case, and avoid the whole pile of formalities and fees associated with the I-485.
But because you are a derivative through your parent, once you get married the original I-485 will be null and void. So you will need a new I-485, with a new medical, new fingerprinting, new I-765* and everything else. There will not be a fee for the I-765 or I-131, because your new I-485 is after the Summer 2007 fee restructuring, which made the I-765 and I-131 free with the I-485 (of course they're not really free, just built into the enlarged I-485 fee).
For your status, write "pending AOS" and leave expiration dates blank. But if you traveled outside the US and reentered with Advance Parole, you can write Parolee if you prefer (I won't get into the details now, but there are some peculiar benefits to parolee status due to nuances in the law).
You can get the medical done ahead of time, you don't need to even be married to visit the doctor for it. You'll need to make the appointment for at least 2-3 weeks before getting married, if you want to get the sealed results soon enough for you to be able to send it with your I-130 and I-485 right after the wedding.
Write 0 for 21(c) or leave it blank.
*you can keep using the existing EAD to work until it expires or USCIS gives you notice of canceling it. Don't request a withdrawal of your old I-485. Let them figure it out and take their time to cancel it, as you don't want your old EAD cancelled before the new one is approved. And once you marry, don't travel with the old Advance Parole, as it would be disastrous if they cancel it when you're outside the US.
Last edited by Jackolantern; 18th June 2011 at 06:26 PM.
EB3 ROW I-485 Approved: July 2007
USC: July 2013
I am a layman, not a lawyer. What I write here is not official or professional legal advice. In addition, my answers on this forum are specific to the scenarios discussed in each thread and should not be generalized to other situations.