The PD must be current and visa available. For PD of 2012, add 12 to 15 years. Maybe longer.

The correct fee is $495 and includes biometrics exam.

The surviving LPR may apply for citizenship when eligible.

You may consider seeking new admission at a land port of entry with all pertinent documents and valid passport.

A subsequent employer cannot file I-485 based base on another employer approved I-140.

USCIS will provide a response in the stipulated timeframe.

In general, for AOS a police clearance is not required.

Consider getting a lawyer to help in exploring other non-immigrant options.

Try congressional assistance and USCIS ombudsman office.

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There is no need to staple supporting documents. Organization is key.