Applying for EAD on H4

I converted from H1 to H4 a couple of months ago. My Husband’s I 140 is in process.

  1. When can I apply for EAD ? Can we apply while Husband’s I140 is still pending or only after its approved?

  2. If we need to file for an H1 extension then can we file H4 extension along with the EAD for me or do I hve to again wait to get H4 extension approved before applying for EAD?