F1-H4 COS and H4 EAD

[dds24]

Hello,

I'm on H1-B visa and have an approved I-140.
My spouse has a pending H1-B petition (status is level 1 wage RFE currently) and can only work till OPT cap-gap end date (Sep.30, 2017).
I'd like to know if we can file for a Change of Status (COS) from F1 to H4 while the H1 petition is pending so that we can apply for H4 EAD to continue working in the States.

Also, how much is the processing time for COS if we do it in the States? Would going to the home country and getting a H4 stamp be a better/faster idea?
If we choose the latter, is it mandatory for me to go with my spouse for conversion to H4?

In the event that my spouse's H1-B gets approved (after response to the RFE), do we need to withdraw the F1 to H4 application?

Thanks!