You may show them your marriage certificate and I think they will probably understand.

Perhaps try to change to B1/B2. If you do not pay for all of the medical expenses, expect for there to be problems returning to the U.S.

No, you can stay out until the visa expires.

If your mother can file directly at the embassy abroad it may be faster. Depends on the embassy or consulate in question.

It is not likely to have any negative impact on you in the future.

Yes, it's okay. You only need one I-485, not one for each I-140.

There is no legal limit. So long as you maintain valid B2 status and file timely applications for extension of status, and your passport is not...

Very interesting. When you get the decision, you should see what it says.

You can certainly try. It may depend on how many dependents there are. When you mark that the current income is zero, it may raise questions.

There is no set amount of time to review a case. No doubt it depends on what the issues are that CIS is reviewing.