Yes, travel is permissible because Guam is part of US.

ASC would go ahead with biometrics examination with appointment letter. Try that and see what happens.

As an immediate relative concurrent filing for AOS is permissible. Good luck.

The receiving embassy must be willing to accept case. Then contact NVC to complete transfer.

Is there any valid reason your wife cannot become USC? Becoming a USC helps in immigration.

Travel to India is expensive and unnecessary. You may work for new employer and show your immigration documensts.

You may have a complex case and must consult with a lawyer ASAP. I don't see how spending time on public forum helps.

There is a backlog on the I-751. It is OK to travel with all appropriate documents.

Go to your interview and present new passport to visa officer..

The I-751 must be adjudicated before a decision on N-400. Follow up on I-751.