Let them set up the LLC themselves and if they are employment authorized, let them work for it.

I would predict USCIS may be very slightly sympathetic.

Yes, there are two separate receipt notices.

You can file, but the court will want to know that you have done everything you could outside of court, and that it is long beyond the normal...

You could contact Customs and Border Protection for help. But meanwhile, your visa and entry stamp are sufficient to prove your lawful admission.

If you are in U visa status, you can file for adjustment after three years of continuous U visa status.

You can write "self employed" if your business has no name.

Both categories are available so I see no advantage, but if you wish, you can certainly notify the U.S. consular officer that you naturalized.

If your H1b is not expired, you remain an H1b until your change of status is granted.

Yes. You can check the USCIS website at uscis.gov.