H1B transfer from company A to B while GC under process

[rk78007]

Hello Expertise,
I would appreciate your input/suggestion for my below queries.
I have been working with company A from last 7 years and I-140 was approved in 2012 and my priority date is  May-11 under EB2.
My H1B extension will get expire in Aug-2018.

In this situation, I am planning to look for different company B. On this regard I have some queries:
1). Is it a good time to change the job from company A to company B while my H1B extension is getting close.(Aug-18)
2). If I changed the job, do I get  my extension for next 3 years while H1B transfer. Or do i need to apply transfer plus extension simultaneously in order to get an extension.
3). if my company A revoke my I-140. Does it affect for H1B transfer & extension. If not do i get the same priority date?
4).Is it necessary to have job responsibilities same in order to get approval for I-140 applied from company B?

Thanks,
RK