H-4 Visa

Previously I was on H1B when my I-140 was approved. Currently I am on H4 status, not employed and my priority date became current.
Previous employer has provided Supplement J and I have filed I-485, I-765, I-131 concurrently. The Supplement J indicates (#9 in Part 6) I am not currently employed with the sponsoring employer.

Q1) Upon receiving AOS EAD, can I directly join a new employer after 180 days of pending I-485 if sponsoring employer doesn't have any open position?

Q2) Can I start searching for new job before 180 days of pending I-485, but join after 180 days? Or, I must have to start searching and interviewing for new job, only after 180 days?

Q3) At the time of filing AOS, my Supplement J indicated that I am not currently employed with the sponsoring employer. If I join the sponsoring employer upon receiving EAD, then do I have to send USCIS new Supplement J indicating that I am now employed with the sponsoring employer, knowing that it might take a decade for my Final Action Date to become current and I may not be employed with the sponsoring employer at the time of GC interview?

Q4) What if I need to change my employer after GC interview, but before receiving GC?

Q5) I heard, after 180 days of pending I-485, even if I change my job couple of times, I can take the Supplement J only from the employer with whom I will be working at the time of GC interview. But can I still send new Supplement J to USCIS from each employers everytime I change my job? Is that legally allowed? or, is there any concern? Because, it might take a decade for my Final Action Date to become current and within that timeframe I might have to change job 2-3 times.

I am on H-1B & my wife also on H-1B. After three months pregnancy leave my wife is planning not to work and to transfer from H-1B to H-4. She will not have last paychecks copy for three months so will it be an issue during transfer? Will she need to start the job again to get three paychecks copy ?