Max Out soon - PERM with new employer


I am currently working with H1B visa which max out date is May 2021. My current company stop PERM processing. So got a new employer who are agreed to file PERM. If they will start filing PERM on Nov 2020. Is this enough time to get the PERM approved and I-140 Premium approved? I have couple of more question also -

If I have to leave the country after max out then what is the possibilities to come back after i-140 approved?

Suppose if I leave the country after my max-out and my PERM is still not approved. After reaching my own country once my PERM approved then can my employer file i-140 while I am outside?

Suppose if my PERM is approved and waiting i-140 approval during my max out can I stay here with other visa like B1/B2 until i-140 approve and new H1B extension? What are the risks are in this?