Yes your friend can financially sponsor you.

The transfer indicates NVC currently has your case and next steps will begin once visa becomes available.

Yes this appears to be sufficient based on information requested.

Once the visa becomes available, you will pay fees to NVC and start next steps.

No not without a waiver of filing through LPR or wait until spouse becomes USC.

Yes you can obtain DNA records to show relationship and provide in new filing.

That is a personal decision but if you divorce, you will need a waiver of the joint filing requirement for I751 purposes.

Consult with a family law attorney to initiate a divorce.

You may answer this question as no based on information provided.

Yes you may apply 3 months prior to 3 year anniversary of GC issuance date.