I can’t really answer most of your questions, but I can just point out that some of these things are not mutually exclusive. For example the Skeletal Mesh Editor appears to be/use FPersonaAssetEditorToolkit, but it also can host UEdModes that use the ITF. If you look at USkeletalMeshModelingToolsEditorMode, this is a plugin you can enable that adds some modeling tools to the Skeletal Mesh Editor, via ITF/UEdMode.
(I was not involved in this and can’t say quite how the classes/etc are set up, though. I’m not familiar at all w/ the Persona or WorkflowCentricApplication systems)
I believe a UAssetEditor can also host multiple UEdModes, similar to the main level editor. This is (relatively) new functionality and has not been heavily exercised though, and I can’t think of any Asset Editors where I’m sure it was done this way.
Sorry I can’t be more helpful. The things you are trying to do are quite complex and not something that a large number of people have had to figure out how to do, unfortunately that means it can be quite hard to get solid information.