Your status when entered U.S., such as F-1, J-1, H1B etc. It may not be the currently status if you changed staus while in U.S.
2) Can anyone kindly provide a checklist?
You can apply AP after or with I-485 (before Oct.1). If this is the first AP, just make copies of everything that went with I-485 and attached them with I-131. That was how my I-131 was prepared.
3) I am still in J-1 status. May I transfer to H-1b after the submission of I-485 (submitted before Oct. 1)? I know the consequence of what I will face if it is denied but had no choice. Will the use of AP have any adverse effect on the I-485 process?
I am not sure,don't you need to waiver J-1 first? But use of AP should have no effect on I-485 process.