This also is part of the EAD instructions:
"NOTE: If you filed a Form I-485, Application to Register
Permanent Residence or Adjust Status, as of July 30, 2007, no
fee is required to also file a request for employment
authorization on Form I-765. You may file the I-765
concurrently with your I-485, or you may submit the I-765 at a
later date. If you file Form I-765 separately, you must also
submit a copy of your Form I-797C, Notice of Action, receipt
as evidence of the filing of an I-485 as of July 30, 2007."
http://www.uscis.gov/files/form/I-765instr.pdfAlso, regarding the AP, if it gets to be within 120 days of the AP's expiration date, you can refile I-131 to receive another one. This would only be necessary if it took more than a year to get a GC. You would have to submit a copy of your NOA from the I-485 to show AOS is still pending and the second AP filing would also be free of charge.