I don't have a list of what opens where. I just went round and round the place trying to remember if anything had changed, and if I thought it had, I explored it. Maybe I should have taken notes, but I didn't. You are right in thinking that there is a button in each of the corner towers, and they all have to be pushed. So 10 levers, and 4 buttons.As a last resort, there is a map at Flamestryke's site - link below. On the Town Portal map on the opening page, click on the "Plane between Planes", and when that comes up, click on "Escaton's Palace", and you will find a map. That will at least tell you where the things are, and which doors can only be opened by pressing or pulling something.