I did it at SFO 3 years ago

1. Take non-immigrant line since you haven't got GC yet.

2. Immigrant officer will take you to a small room, where your passort and AP will be stamped. It took 15 minutes in my case, no fingerprint and no question was asked. No other documents were required. Someone suggested to take I485 receipt but the office didn't ask for it. I brought two APs I had and got both back.

3. I only used AP once so I don't know answer for your last question.