Yes travel is okay with the documents you indicated.

Best to have an attorney review the specifics of your case.

No this alone isn’t a basis for visa approval.

More information is needed about the delay. Consult with an attorney for guidance.

Wait for the decision from USCIS as there is no other recourse.

Just wait and see. Worst case it’s unlocked and you submit whatever minor error needs to be corrected.

Yes despite income, the petitioner must still file the I864.

Once the priority date becomes current, the applicant may file.

This can be easily corrected at the time of interview without issue.

Best to have an attorney review your case history for better guidance.