It's your call - 回複：Dependent's petition will be mailed - 回複：副申

whether you go with your I-140/I-485 then spouse's I-485, or your I-140 then your I-485/spouse's I-485.

I don't see big difference at the moment.

You may need to read this http://web.wenxuecity.com/BBSView.php?SubID=immigration&MsgID=332442