Questions about H1 transfer, H4 EAD and GC

Hi Guys, I have a few questions that I am trying to find answers to.

  1. I am currently with Employer A on H1B visa(expires August 2022). I 140 priority date is September 2018.
  2. My wife has a H4 EAD through my I 140.
  3. I have a new job offer from Employer B.

Questions:

  1. Is it necessary that the new employer has to start the GC process again or they choose not to do it?

  2. When the new employer applies for H1 transfer, is it automatically extended for 3 more years from that date. If that is the case, we don’t need I 140 any time soon. Is this right?

  3. My wife’s H4 EAD expires August 2022. Does this transfer affect her EAD in any way? And can we apply for EAD extension if the new employer doesn’t file a new GC process?

  4. Filing the GC process again changes the priority date? What are the things I need to keep in mind here?

Thanks and all the help is appreciated.