I thought Zero-God, Solitary God, and God of Gods all were different ways of talking about "all the agencies of the Outside" (as well as the Dunyain concept of "The Absolute"). Maybe "unified" to lesser or greater degrees.
I think Ciphrang and The Hundred are basically the same thing. Agencies in the Outside capable of manipulating souls. The big difference I see is that Ciphrang don't seem to have the same perceptual weirdness as the gods (seeing the future, not seeing the souless). Although that might just be because they are currently Inside, rather than Outside. Maybe perception in the Outside is tied to soul rather than place ("soul became place" in TTT, though that's probably not strictly relevant). When you look at a soul in the Outside, you see that soul's whole existence, from creation to destruction. But you can't see stuff that doesn't have a soul. Which explains why the gods can't see Sranc.