Get married first.

Once you get married, he can I-485 with you at any time after you I-140 and the priority becomes current. It is OK even after you get GC.
For your case, nobody knows when your priority will be current. To keep his job in Japan, it is better for him to get married with you as soon as possible and go back to Japan waiting the priority.

請您先登陸,再發跟帖!