In the He Who Fights With Monsters Multiverse they show us an example of how the multiple layers of reality function with the interactions Jason has with the fundamental realm. I feel this leads to a different and interesting interpretation of how the planes could and should work in this setting.
The elemental planes are not unique and infinite metaphysical planes that you can leave your world to go to, and there are no outer planes. Instead the planes are different layers of reality and shifting between them is like moving in the 4th dimension up and down the scale of energetic power.
The plane where the gods reside, where positive mental energy sent out into the world goes to feed the gods with prayer. The Gods have a small amount of control over small regions of this plane but it is almost entirely inhospitable for mortals. This is also the realm of creation, where pure energy from the either enters the world and is filtered down to the other planes of creation.
The Fundamental Realm is a high energy plane that hold the building blocks, or something akin to the DNA of the universe. A cubic landscape filled with blocks that hold the power of law and order, used to describe how the rules of the universe should function and maintain it's continued operation.
The plane of fire is where plasma is born from the either and where even solid materials reach such high temperatures that they can't exits anywhere but within the heart of a star. A blasted wasteland of stone and metal. Living things on this plane are comprised of flame, lava, blackened metal, and magic itself.
The plane of air is an endless sky, with areas of empty blue, and others filled with clouds, some white and fluffy, others black and charged with energy. The air can be placid or it can be tempestuous. And while most of the plane would be breathable to mortals, there are areas filled with portions of what we call air that in high concentrations would be poisonous, or simply lack the elements we need to survive. There are areas of land, built on a type of magically charged stone that is neutrally buoyant in air, and most creatures if not part air or mist, have at least some way to fly through the plane.
The Material realm is the nexus of all the meta-planes, where all their influence is directed to create and maintain the balance of the world we all live in.
The plane of water is an endless expanse of water. Filled with creatures adapted to live in that environment. There are pockets of stone or air that exist on the plane but they are rare amongst the currents of the vast plane. Some areas are fresh water, some are salt, some are more acidic while other's are more on the basic side. The vast majority of the water is a livable temperature, but there are areas where the water reaches temperatures well above the boiling point but have no where to go, or well below the freezing point.
The core of the plane of earth is mostly dirt, an almost endless expanse of dirt and stone. There are areas with different types of earth or stone. Areas that are primarily marble, sand, granite, obsidian, fertile soil, or barren salted earth. There are areas where gems or precious metals grow unnaturally fast, and areas filled with things like alkali metals that if exposed to air could set off an explosion that would level a city. The Plane of earth is almost entirely solid matter, pockets of air or water are few and far between.
This is the plane where demons reside, creatures of malevolent intent born of negative psychic energy, dark prayers, and vices. The Negative energy plane, being the demonic plane, has a decayed, corrupted, landscape filled with alien demonic lifeforms in a constant state of war. The negative energy plane, is very hostile to living matter, anything within the plane is exposed to radiation and begins to break down on a cellular level. Demons summoned to the material plane often exude a level of radiation.
The Void is the realm of destruction. Nothing lives here, there is no solid plane or creatures, or gods. There is nothing but that wIs where any ejected matter from the other planes ends up to be converted back to energy and any excess energy funneled into the system is filtered down into. From here all energy is expelled back into the either.