I now have the outer plywood glued to the cores. I used PL and troweled it on with a notched trowel. Then I walked all over the wall and then loaded it with milk cartons filled with water. I do believe it's well bonded

I did have one very unusual situation. I ran out of glue just before I finished applying it so I cut the tip off a new tube and then tried to put it into the gun. It would not go in! It was too long and would not fit.
I worked on it for about ten minutes while the rest of the glue was setting up and I was running out of working time. I finally pounded it into the gun and finished the glue up but I've never run into a situation like that before and at such a critical point

I'm now ready to move on but I have a question: Is it better to put the finish on the walls before you put them up or after?
I'm thinking before because it would be easier to do with the wall lying flat.