Does H4 appl. depnd on H1B Extn pendin(140-Aprvd) ?

My Spouse applied for H4 ( change in status H1B->H4) on my H1B extension application. My I140 is approved. 1. Please advise whether H4 application depends on H1B extension approval? If my h1B extn is not yet approved, so H4 application will not be approved? It’s been 4 months already ( rcvd H1B extn receipt on July 21) and I have not received any response yet. The processing times it states- June 21 upd on Aug 31’17.

  1. Is it good to do premium processing for my h1B extn application now or should i wait?

  2. How long would it take H4 appl to be approved after my H1B extn appli approval.

  3. How long would it take H4-EAD to be approved after above item#3.