You can contact an attorney using the Avvo search tool.

Sibling based petitions take 15 years or so.

Yes this is possible while I751 is pending.

Yes contact USCIS to inquire directly.

It can take 1-2 years for AOS through marriage.

This can be corrected at time of Interview.

Best to contact USCIS to inquire further.

Consult with an attorney to review your case and determine next best steps.

Yes but you should receive it by mail.

Yes you should be okay to travel with the passport and current status.