Your sponsor must still file the I864 and you will also need a cosignor.

You can use the Avvo search tool for assistance.

Yes you will need to do a waiver and should file within the necessary timeframe. You will still receive an extension despite waiver filing.

If you are eligible for EAD then yes that is possible.

Yes this will be scrutinized so expect questions re: first marriage.

Best to work with an immigration attorney for case specific inquiries.

Yes with validly issued EAD, that is okay.

That is not possible at I751 stage.

Yes you should indicate the A number for filing.

Yes you should expect that decision should be made soon after submitting.