Depends on the law of the state where you reside and get divorced. Some states allow "nunc pro tunc" to your marriage date after divorce and other...

Your selection is based on your country of birth so select that box.

That is fine -- you are eligible based on country of birth, not country of citizenship. You can then process in any country where you can remain...

You may report it as fraud and/or file for divorce and allege fraud and USCIS should pick that up next time she files to remove conditions on her...

Once you have entered on an immigrant visa you have a one-year stamp to travel while awaiting the physical green card.

If you want to resume going to school, you need travel I-20 from the school and you will need to get a student visa to return; if done with school...

You can explain just as you did here -- that you were a derivative on a petition filed by your mother that was discontinued.

You can satisfy with sufficient tax return from previous year plus either current income or 3 times the assets for any shortfall.

We need more details. USCIS will look at the most recent tax return for your joint sponsor and their "current" income. If not sufficient, joint...

You can go through a state court procedure here or contact your home country's Embassy on how this can be done.