If you earned enough to meet the filing threshold, you must file back taxes for the 3 most recent tax years. All US citizens and legal residents are required to report world-wide income regardless of residence and/or work location. Your case will not proceed beyond NVC until you provide evidence of tax filing (if required to have filed).
This is close to correct. You, as primary sponsor, must file an I-864 with supporting documents, and you will need a qualified Joint Sponsor to also submit an I-864 with supporting documents unless your qualifying foreign income will continue after re-locating back to the US. Remember, the minimum income level does not mean accepted income level. The Consulate officer could require a higher level based on the totality of your situation.
Unfortunately, that ship has sailed. Since you have already filed the I-130 with USCIS, you no longer qualify for DCF.
You will have to either show proof of concrete steps taken to re-establish US domicile, or you must move back alone and establish domicile.
In summary, you have 3 areas to work on:
-Taxes
-Qualifying income or well-qualified Joint Sponsor
-Domicile
Each of those is a show stopper at NVC and the Consulate, and it appears you are rapidly approaching the NVC stage.