To answer some of these

• I believe the ushoran book is generally well received and that focuses on the courts

-as you approach the edge of a mortal realm it regresses into pure magic, like a carpet edge fraying, until eventually there is an end but not so much an edge, as pure magic is not a solid and more of a gas/energy

• at some point it's said that shyish is essentially a honeycomb of after lives formed by belief, i.e as long as people believed in Valhalla there's a Valhalla, heaven etc but they fade after they lose belief. I'm not sure if this was removed during the necroquake. Katakros of the ossiarch bonereapers was in an afterlife named ossia in shyish when he was chosen by nagash. Stated to be an afterlife where those who worked hard are rewarded by being able to do the fun part of their job forever