Under the current laws, if you change jobs after I-140 approval you keep your priority date, but you lose your right to H-1 extensions beyond what is given if your old employer revokes/withdraws the I-140.
Now answering your questions
Answer 1.No, you will get an H-1B extension for the time remaining and you can actually claim one year extra if your PERM was filed more than a year ago. But you will get only three years if the I-140 is approved. Not if it is pending.
Answer 2. I don't recommend it. I think you should get your I-140 premiums, get it approved and then leave if you want to.
Answer 3. I don't think that is a major issue, but do talk to your lawyers. Hence it makes sense in my view not to change until the I-140 is approved.
Note: This is a verbatim transcript of the referenced audio/video media delivered as oral communication, and, therefore, may not conform to written grammatical or syntactical form.
I have answered my H1B Extension RFE with Rajiv's office. They were great in getting the work done and respond back quickly from their side. They will also answer very promptly for any immigration or rfe document related questions. I would like to say specially thanks to Jagbir... who did a great job on his part and answered all the questions in detail. His timely updates & and his timely emails reminding the timelines are really very appreciable. Thanks for all the effort --- Venkat