It won't stop moving downwards because you put the Switch operation inside the Move command in your second page. If the switch operation is part of the Move event, it will ignore it while parallel process is on. Delete the Switch inside the Move event, and create a separate command (a normal switch operation) below that, so it will perform the switch right after the box moves. Make sure the second page IS on parallel process or it won't work. Then the third page can be the chest where you get the treasure.
Chests CAN move. Just make sure that it doesn't animate when it moves, or it'll look kinda silly. But that's it. I've tested it out and I got it to work for me, so hopefully it'll work for you.
Good luck.