What type of petition will your husband be filing?

She will need to provide a statement for failure to file taxes and/or she was not required to do so.

It means that your 10 year GC is being mailed to you.

Yes the biometrics will still be required unless waived.

Your USC spouse may petition for your son as a stepchild of USC.

No not for employment based immigration.

There is a visa available but eligibility must be met for applicable and subsequent approval.

Contact USCIS directly to request the extension.

It may be but likely should not impact the case.

This should be the current income as indicated on your most recent tax return.