The Primordials
Born in the echoes of creation, they shaped all living things, wound into our very essence. Yet, left unchecked, they will be the end of everything.
In the beginning, there was nothing. Then, from the swirling chaos emerged primitive things, the ancient precursors of life. Little more than self-replicating machines, driven by simple impulses, the distant prototype of desire. In time, these entities spread, and their impulses began to form a pattern - Consume. Replicate. Survive. Though they could hardly be called thoughts, these drives nevertheless imprinted themselves on the fabric of the cosmos, the primitive prayer of a primitive thing. And so the cosmos responded, their echoing cries carving into existence the first Gods - the Primordials. But the Primordials were but an ancestral relic of a God, driven not by concept but by antediluvian compulsion. It could not yet form a divine will, existing only as a shadow. Still, as life grew, so did they, and as life spread, so did they. And as life advanced, so too did the Primordials. The first thoughts of beast and man dripped into the ocean of inchoate desire... and gave it form. Gave it purpose. No longer was it a shapeless abstract, but an endless, infinite yearning. And wherever it found its like in the physic worlds... it reached out. Modulated by the structure of sapient thought, at times the Primordials would surge into the world - like the miracle of a true god, but far more powerful - and persistent. They took, and they gave, reshaping whatever they touched, an image of desire reflected in the waters of ancient drive. Those taken by the Primordials reshaped them in their own image, just as they were reshaped in turn, and became Abominations - the heralds of the Primordial, creatures twisted to embody utterly the primeval desires that drove them in life. Fortunately for the multiverse, with the coming of will came myriad other desires, not dominated by the Primordials. Their very purity forms a powerful obstacle to their influence, since it requires a simplicity incomprehensible to sapient beings. Nevertheless, the outer reaches of the Primordial, home of their children, the Abominations, can be drawn by strong enough desires, when the planes are aligned - worse still, terrible magics can call out to them, forming a link by sheer force. Where the primordials touch, worlds die. Civilization dies. Thought itself dies in the wake of all-consuming desire. They can be fought, yes, though not by normal means - yet remain an improbable though terrible threat, lurking beneath the surface of all cosmos. There are three primordials, which all go by many names. They frequently interlink, and many Abominations exhibit the influence of several. The first is concerned with maintaining one's own survival at all costs. Quality does not matter, form does not matter, the survival of others does not matter. It is life distilled down to raw existence, forests of crystal frozen in time. This is likely the least dangerous of all primordials... yet nevertheless can have a terrible power filtered through the lens of sapient existence.
The second is concerned with consuming everything possible - a never-ending hunger that devours without distinction or remorse. Greed is nearly too complex an emotion for it, and it appears somewhat rarely, usually alongside the others. It rarely leaves anything behind, having consumed all its path. It is the world-view of a black hole.
The third is concerned with self-replication. This can come in many forms, and in its purified state may take the form of exponentially spreading plagues of Abomination, but is more commonly filtered through the lens of lust, a desire that must be fulfilled regardless of the consequences. The most virulent of the Primordials, and oddly, the most relatable.
Geography
While, obviously, it is difficult at best to 'map' the Primordial planes even in part, they can generally be divided into four layers. Outermost is the point of actual contact with other planes, where it exerts its influence, slowly working to transform its surroundings into something more like itself. Within that is the Primordial surface, consisting of space-time that has been successfully absorbed, its inhabitants transformed into Abominations. In this layer, existence can proceed in a relatively normal fashion - with consistent laws of physics and everything, perhaps even something resembling Cytan society, although the overweening will of the Primordial watches over all. The 'deeper' within this layer one travels, the more distorted things become. Most incursions originate from around the middle-depths of this layer.
At the third layer, existence has been altered by the primordial so thoroughly as to be unrecognizable. Its will is law, and there is barely a trace of whatever came before - if anything. Nevertheless this level is - barely - comprehensible by Cytan minds, although anyone unfortunate enough to do so will no doubt wish they hadn't.
The final layer, theoretically, is the essence of the primordial itself - it cannot be observed or comprehended because it really isn't anything at all, save the formless essence of the primordial's desire, shucked of all form, interpretation, or purpose.
Fauna & Flora
Besides the myriad Abominations, there are creatures created by the Primordial itself - which, confusingly, often also get lumped into the category of Abomination, but are more properly called Primordial Entities. These Primordial Entities are aspects of the Primordial's existence, and cannot be separated from it. They are, as a rule, more alien and more pure than Abominations, which ultimately originated elsewhere. The purpose of the Primordial Entities is to fulfill the will of the Primordial, and those that exist in the upper layers are often found to act as 'enforcers' - or shock troops, when the primordial contacts another plane.
Natural Resources
As a general rule, you don't want to get anything from a Primordial on you.
Of course, it might be valuable, but it'll possibly come at the cost of your world, not to mention your sanity.
Type
Planar Sphere/Grouping
Okay so formatting is needed for this. I would add some headers or something to the big block that came first. The list of the gods could use spaces between paragraphs. The geography could use to be broken into paragraphs. I found myself getting lost in the text of that section. The ideas are interesting but I would like a bit more description on things like how one might contact or reach these planes. I would also like some idea as to why anyone would be so foolish. It is an interesting idea that needs some polish to make it shine. But keep up the good work.