[Gromit]

Can't answer all your questions but I do know to make sure you open the tailgate and remove the nuts that fasten the very outer ends of the upper trim (on the inner side of the tailgate).

I believe that the rest of the fasteners are best removed using one of those nylon trim remover tools and a very small pick. You lift the trim slightly and slide the point of the pick behind the trim to catch the end if the spring wire and allow it to unhook it from the well in the trim.

Once you see one you can do the rest...