Yes, helping someone, even a relative, file an application makes you the preparer.

Yes you can notify NVC where you live and if you get scheduled in the wrong country you can notify the US consulate abroad to send the application...

Bring it to the interview and submit it then.

It depends on the office and the officer. Generally it would be recommended.

File for a reentry permit next time you come and you can stay out for two years. If you will not be living permanently in the U.S., you may wish...

Find a criminal defense lawyer to un-expunge your convictions and get copies of your records and then file to renew your card.

Yes you need to list them and provide certified copies of the judgments.

There are never any guarantees and there is always a risk of denial.

Yes it is normal. You can file a FOIA request for them if you want them.

The pay stubs should be fine unless your W-2 at the end of the year shows that you were not paid the amount you claim.