Amazing how much is discovered when you peel into one. When you’re done it will be so much better than new. As for the transom/core question I would run the transom down all the way and glass it in first. I did a system of increasing my edges by 2” and in come cases 4” meaning if I put three lays of 1708 over the transom each piece ran out 2 or 4 inches wider than the previous. I would do this down to the hull too so the transom glass runs under the core. I put a ton of glass on my transom but I think I have three layers down the transom under the core. My thinking was the more glass the more strength and especially around the rear of the core more to protect the core in its most sensitive place. The back two feet of the core are doing all the work when running wfo