1) Am I legal after I H4 application before H1B expired?
-Yes.
2) After H1B expired and before I get my EAD card, to keep my job, can I take unpaid leave or work as volunteer, is legal?
-No.
3) After H1B expired, if I have used EAD and our 140 gets denied, what are the options to maintain my legal status?
-Get an H4 visa outside of US to get H4 status if your spouse still keeps his/her H1 status valid.