I-140 approved, I-485 pending for 180 days, new job should be in same or similar classification

No restriction on investing in the business, but you cannot run the show for the company

It is a one step process. You don't have to first file for COS.

As long as you are employed, you are good

You lose your visa and will have to apply for a new one

If COS is approved, you will be required to maintain H-1B

You can depart. Seek B-1 for this visiting role.

Either employer files COS or you enter on H-1B to work on H-1B status

You can be member of LLC however you cannot be an independent contractor working for the LLC

Your employer can start the process, when approved you can consider VD.