我见, or other DX, please help!!

Now I got my I-140 approved and will file 485 soon.
I got another offer and will move.
1. Should my hu*****and change to H-4 before we fill 485 or he can do it after we file 485?
2. if my hu*****and hold H-4, can he use EAD to work? If after he used EAD and our 485 denied, can he still keep H-4?
3. Is it possible that BCIS deny our 485 after 140 approval?