Hey Beefy amigo!
What's interesting is I actually made different rules for all the different planar dimensions (not spacetime dimensions) an Immortal can make their realm in.
Cool.
I actually made Byss the most safe, it's the realm of death, of nothingness, so nothing happens there and your realm never grows, it's just stagnant, not that it's without danger, but comparatively it's safe.
Entropy being analogous for a universal cancer means that it grows by virtue of other realms succumbing to it. But certainly there is a tangible malaise and apathy congruent with that dimension.
I don't want to give too much away yet but in my version 'Byss' is primarily the physical border between Entropy and Reality. That's where stuff actually still happens - albeit by these crazy new monsters and factions I'll talk about in the book.
The other realms grow more and more dangerous as you move up vibrationally, the outer planes and far place being the most dangerous.
It makes sense for each dimension to up the ante and the power level.
In some ways think of the dimensions as a massive kosmic dungeon. Moving from one to the next is like going deeper into a classic dungeon. The threats are increased, but so to, the rewards.
The outer planes being the realm of the gods is actually pretty safe but since there are gods, abominations and neotic and adamic dragons there, it can be very dangerous.
Certainly the outer planes or wherever can have hostile inhabitants who are dangerous. But I think that is different to the dimension itself being hazardous to the health of immortals.
Plus when you think about it logically, gods would not choose to dwell in places where they were not top of the food chain. They would not dwell in places where they were under threat all of the time.
So the Far Realm may be an interesting place for powerful immortals to go adventuring. But they would have to be mad to try and live there.
The Abyss I have actually split into three places, the Infinite Planes of the Abyss like Hell, os the realm of chaos and evil, The Far Place is the infinite planes of madness, and The Green Realm is the realm of Chaos and Good, it's the land of the Fey and also considered the dimension of Life.
I don't think there is a right or wrong way of structuring the outer planes any more.
I do like the streamlined simplicity of the 4E model where the Astral is the home of the gods (and devils), whereas the Elemental Chaos is the home of the Primordials (and Demons). But at the same time I always loved the Great Wheel, especially for the lower planes.
Either way I am sort of leaving out the Astral/Outer Planes and Elemental/Inner Planes from my new Kosmos Chapter. To explain, I don't mean 'leaving out' as in they don't exist. I mean leaving out in terms of they have been so thoroughly explored that I really don't need to further write about them in my material. At least not beyond the bare basics.
Whereas places like Byss, the Far Realm and the six other dimensions I WILL be detailing, are either completely new concepts or conventionally misunderstood places (like the Far Realm).