H1B - petition transfer from one company to other


Please help me on the below queries.


I am currently working with company A in India and my H1B petition got approved. I am planning to join company B. I will get my Visa stamped under company A in next 2 months. 

When I transfer my H1B petition to company B do I have to get a new visa stamped again or can I use my company A visa stamp in my passport (once get)  to enter into US ?


1. Since, I have decided to change with company B,  whether company A visa stamp in my passport (once get) will create any issues/impact, If I have to appear for visa stamping for company B, if required ?

2. During visa stamping for company A, if US consulate rejects .. still I am eligible to transfer my petition to company B ?

3. Do I need to wait for a particular period(months), after company A rejection by US consulate before appearing for company B visa stamping and transfer initiation ?

4. Is there any risks involved in this transfer process at later stages?  Or is it recommended to proceed ?

5. Is it ok to start the H1B petition transfer process for company B, while still I am working in company A in India?

6. If company A cancel my petition after I quit, within how many days, I have to apply for transfer with company B ?  Is there any period for the cancel and transfer process ?


Please let me know your opinion.