A certificate of naturalization is always useful if can be obtained.

Working on the EAD through AOS will impact your H1B.

Wait for the next scheduling which could take weeks or months.

Contact USCIS regularly to inquire and move the case along.

USC may reside outside of the US indefinitely without consequence.

You can attempt expediting but likely will not be responded to.

Best to consult with an attorney to review the specifics of each process. Good luck!

The divorce will result in I485 denial if case based on marriage.

No not based on the 30 years absence.

Yes you may explain the situation and provide some documentation of GC approval.