Because your H1b was approved for 3 years and you spent two of those years outside the U.S.

You can go to India and reschedule if you get scheduled for an interview.

Yes, it puts her in danger of being removed from the U.S.

No. If the H4 is no longer the spouse of an H1b, the H4 cannot be admitted as an H4.

It depends on your age and marital status.

If she was over 18 at the time of your oath ceremony, she needs to file her own N-400.

If the visa is available, yes, it makes sense.

You can be issued the immigrant visa outside of the U.S. There is no requirement to get into the U.S. and then adjust your status once you are here.

Since you do not need to be in status at all to file for adjustment based on marriage to a U.S. citizen, there is no need to wait for any decision...

If you do not qualify for Child Status Protection Act, then you may be an F2B. But if you do, you remain an F2A.