H4-EAD extension during H1 and H4 extension pending

[Sathishn]

Hi, 

My H1B and my Spouse H4 and H4 EAD expires on Sep 13 2016. Extension is already filed for my H1B and H4 and i got the receipt numbers in regular processing. Now i am planning to submit the H4-EAD application. 
1) Can I file for my spouse H4-EAD with the receipt and will it get approved with my H1B and H4? 
2) If i can file for the H4-EAD, what is the information should i enter for Q 18 in form I-765? My previous Approved Receipt or My current Receipt of extension filing? 
3) Do I need to send any letter describing the details to the case officer during the filing of H4-EAD? 

Appreciate your help. 

Thanks, 
Sathish