H4 to H1 COS with H1 Extension with approved I140

Hi there ,
currently i am on H4 EAD, i am working for same client for last 3 years(first on H1 and then on H4) . I have valid H4 visa stamp till May 2021.

If I file H4 to H1 COS + H1 Extension (with approved I140) in premium processing in January 2021.

  1. Can i work with H1 Visa without stamping(as i dont have plans to visit India) ?
  2. Do i need to go to H1 visa stamping before i start working with H1 visa(if approved).
  3. If H4 to H1 COS with H1 Extension is rejected, can i still work with my H4?
  4. Do client letter is must for applying H1. If i apply to H1 without client letter whether H1 will be rejected?

Thanks in Advance.

You can work with H1B if it is approved with a new i94.

If its denied, then you can work with H4 EAD if its valid.

thanks Anil for response . As i work as contractor with third party vendor , if my H1 will be approved then it will be only one year extension ?