Form I-485

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 got my GC on March of 2016 through my then employer. Soon after getting my GC my project ended (May 2016) abruptly because of the change at client location. I did not had any project at hand so I started looking for a new job and started to work with new employer in June of 2016. There was no official end date of my employment with my previous employer through which I got my GC because they were looking for a new project for me but without any certainty how long it could be before they can find me a new project. While they were looking for a project for me, I already started working for my new employer so I just moved on without any official end date with my previous employer.

In Feb of 2019, I started a second job with another employer. Currently, I'm working 2 jobs full time on GC.

I am now eligible to file for citizenship through 5 years of permanent residency requirement. I'm worried if there will be any issues while I file for my citizenship because I did not stay with the employer that file my GC long enough after receiving my GC. Also will there be any issues because I am currently working 2 full time jobs when I file for citizenship?