H1B transfer to a new employer before stamping in consulate processing

I have few questions

I was working full time with employer A and attorney filed H1B on April 2017 through consular processing
(since I traveled to india on May for my wedding). Unfortunately my company was acquired by other company on June 2017
and they laid off few employees including me. Employer A didnt withdraw my petition and asked me to get it transfered
with my current employer once approved. Now I am working with employer B and they are ready to file an H1B tranfer once it get approved.
My OPT is valid till Feb 2019.

1). If my H1B is approved do I need to go to India immediately to get H1B stamping for consular processing?
2). My h1b will be with employer A, employer B should file H1B transfer since I not am working with A anymore, will this affect my status?
3). Can I do H1B transfer before stamping?
4). My wife is in F2 and is it okay if she continues in F2 and we file for H1b transfer and H4 together with employer B,
she could not travel since she is pregnant now.