The I-751 is designed to be filed in the US.
Issue #1 is GC holders are expected to live in the US.
Issue #2 even if temporarily living outside the US, LPRs are expected to maintain ties to the US including residence, ideally (rented or owned)
Issue #3 for mailing address, US address preferred. I don't believe USCIS is going to send mail internationally.
From what I saw, many filers in your position use a good stable US address for Mailing Address (not for physical), such as their parents' or relative's house etc.