Know any good lawyers with AC I-140 experience?
Answer: Rajiv Khanna!
Do I have to apply for advance parole or can I travel back and forth on revalidated H-1B visa?
Answer: You can travel back and forth on revalidated visa. But please confirm this.
If I do travel on H-1B, will it be considered an automatic abandonment of the pending I-485 application? (If I get the interview date prior to I-824 approval)
Answer: AOS is considered abandoned at the point in time when you have filed for I-824 and BCIS has sent you a letter to find out if you really want to abandon AOS and move to CP.
Do I have to prove hardships in waiting for AOS?
Answer: Waiting for the time it takes for AOS in itself is a hardship. But if you can complement this with something else that would really help.
Disclaimer: I am not a lawyer. My replies are based on knowledge gained on immigration sites & my studies on US immigration. It is always good to consult an immigration attorney such as Rajiv Khanna. If you have specific questions for me, please PM me.