If a PD retrogresses, the I-485 needs to be refilled when PD becomes current.

Traveling out of the USA while H4 extension and EAD is in progress is not recommended.

It means an administrative action, that should not be a concern to you.

You should work out all that details with your school DSO and employer's attorney.

If your PD is current, file I485 to complete the process. Check processing times on USCIS website.

This is not a direct immigration question. I'll transfer you to lawyers who may help.

Switching the underlying petitions I130 and I485 is not permissible.

Complete Form AR-11 for address change for both petitioner and beneficiary.

Take a non-governmental id and other supporting documents like car registration, lease, bank statement, etc to the interview.

If you are the petitioner, your son needs to be in status for AOS because you are an LPR.