EB2 Future Employment Case, need to change job, H1B or EAD?

[falcon_7X]

I filled PERM and I-140 with company A (EB2) and then changed my job and joined Company B ( I-140 was approved with PD of June 2009 with company A). After working at Company B for about 1 year, just recently my PD became current. I had not started the new GC process with Company B at that time. My old company A helped me and provided me the job offer letter and I filled the I-485 with company A, with the intention of future employment with them. PD has again moved back, but I have got the EAD/TD after filling I-485 with company A. Now things are little dicey at my current company B and there is a possibility of layoffs. Currently I am working on H1B visa with company B (my 6 years on H1B is expiring in 2013). I am not very knowledgeable in this issue; therefore seeking advice on the following questions:

1. For my new job search, should I only look for jobs with H1B sponsor or if I can use my EAD card to get another job?
2. Will it be safe/advisable that I can use my existing EAD card to find another job with another company C?
3. Since currently I am not working with company A, does AC21 rule applies to me (future employment)? The reason I am asking this is to decide, should I specifically look for jobs with company A (contracting house) now to satisfy green card requirements ( if any)? I am not sure as my green card was filled with the intention of future employment, how long and when should I start working for company A ( my main green card sponsor)?

Thank you in advance.