Dear attorney,
I got my GC-labor(PD 23-Jan-2008)&I-140 approved form Company-A.
Currently with Company-B on H1b valid upto 2014.No GC Process started yet.
I want to take offer from Company-C which is put on hold temporarily.
I'm still in good terms with Company-A.They are willing to file my I-485 when PD becomes current.

Questions:

1.what is the best option for my situation? filing I-485 with A or B when PD becomes current?

2.Can I file I-485 and EAD with Company A or Company B and when Company C offers me job can I work for Company C with EAD without filing H1?

3.Can Company B file my I-485 when PD becomes current without filing labor& I-140 underAC21 portability?

4.what is the best option for me to join company-C without any problems with my GC processing?