change of employer with approved i-140, time for AC-21 portability post i-485

Namaskar Rajiv ji!

asking the Qs in forum as yo suggested on Linkedin...

1. my i-140 approved for almost 2 years now and EB-3 India priority dates are far behind, meantime if I change job, new PERM + i-140 needed from new employer as you confirmed. Is it same if you change position/role in same company or get promoted in same role/job description for which PERM/i-140 was approved?

2. How long will H1-B for this new job be valid, if I'm in 5th year of my initial 6yr H-1B period already? will it be new full 3 years as usual, based on previous job's i-140 approval over 180 days? and in that new H-1B time, does new employer have to get new i-140 approved so they can keep extending transferred H-1B further?

3. what happens if dates happen to become current when new job's PERM is in process and new i-140 is not approved yet. Can one file for i-485, once date is current based on old approved i-140 already? Or one has to wait until new i-140 is approved with old/retained priority date and only then try luck to file i-485 hoping date does not retrogress?

4. also independently if I stay in same job with current approved i-140, and dates become current to file i-485. After the i-485 filing, must one wait 180days from that time, to get AC21 portability with supp.J if employer changed? Or right after i-485 filing is OK, since i-140 was already approved 2+ yrs. back?

Thanks a lot again for your help!