Yes USCIS accept the USPS mailbox however you still need to put your physical address where you reside. Answer to you third question is you can put YES so when your VAWA approves they will send you C31 EAD meantime you can send C09.
Congratulations. It is too early to reach out to your congress person as per my experience. I would contact them after 6 months and that's what i did after my VAWA approval. Other than that you will be fine just enjoy the moment. It is a great feeling having VAWA approved after long wait.
Sorry to hear about your friend. Hope everything goes well for him. Also try to contact Sandra as you know she is the best!
I will DM you one of the attorney which i personally did not use however, i have heard good things/reviews about her.
You should be fine without lawyer. They should only ask you yes/no questions. If they ask you anything related to VAWA and you are uncomfortable with it you can always ask for a supervisor.
I have not seen anyone on this forum. However, on the other forums i have seen few people using AP while VAWA pending recently. Their process was smooth.
I have seen few approvals of 2022 in different forums.
Once you move you have to notify USCIS. I would say if it is not urgent then delay until your immigration process is over.