You are not permitted to continue working for your original H1b employer if CIS granted a transfer to B.

Perhaps there will be an interview. Perhaps it will be waived. If the I-140 is already approved, perhaps CIS will verify you are still working in...

There is no way to know that information. Anyone could guess anything.

You have no petition to withdraw. But you can withdraw your i-864.

An extension means you are filing under the same category, not a new category. So no, a C9 application is not an extension of a C8 application.

Perhaps hospital records, school records, other government documents, photos, affidavits of witnesses.

If the only reason you want F1 status is to get the OPT work permit, you should assume you cannot have both F1 status and any other simultaneous...

You can file five years after you got the green card, or three years after your spouse became a U.S. citizen, whichever is earlier.

One does not need to be in lawful status to file for adjustment based on marriage to a U.S. citizen. Rather, one must show a lawful admission.

A pending PERM does not prevent one from getting an H1b visa.