You can simplify the Great Wheel a lot to give you a more streamlined setting.
My primary campaign world has for decades consisted (with only slight evolution) The Prime, The Transitive Planes, The Positive energy Plane, The Negative Energy Plane, The Elemental Plane, The Astral Sea, the Far Realms, Heaven and Hell.
The Prime is centered around one world, but there are other planets in it. You can Spelljam between the planets, but gate magic is more common.
The Transitive Planes Connect the Prime to other planes. Ethereal connects to the Far Realm. Shadowfell connects to the Negative Energy Plane. Feywild connected to the Postive Energy Plane. They mirror the Prime and slowly morph to reflect it more closely, but touched by elements of the other plane.
PEP and NEP are impossible to survive. They are mysteries. Only the most powerful of divine creatures can survive there for even a moment. They represent the Well of Life and the 'Drain of Death' as one player labeled it so long ago.
I have just one Elemental Plane filled with massive pockets of each element. Some of these pockets are hundreds of thousands of miles across.
My Astral Sea is the primary place where Spelljamming takes place. People use Gates and navigating through the Astral Sea to travel between planes, or as shortcuts across another plane. My version of Sigil is here - a floating city where there are thousands of Gates to other planes and places. There are countless pocket dimensions that connect to this plane (used to make Bags of Holding, cast Demiplane, etc... Some are massive - large enough to contain worlds (like the home of the Githyanki).
The Far Realms can't be reached, but it is slowly colliding into the other planes. It is actually an entire alien cosmology. The first collision of the Far Realm with the main Cosmology brought Chaos to the world - turning Devils into Demons and shattering the connection between the planes enough to create the Transitive Planes. Only one being, Cthulhu, has crossed from the Far Realms into the main cosmology, and it is unclear whether this is just an Aspect of Cthulhu or the real deal.
The Heavens are 7 realms where Gods were banished by my original God figure. They are not all great places. The Swamp of Twilight is controlled by three evil gods and is as much a nightmare as the Hells in the eyes of most. A way to think of it as each of the 7 realms are the home of an entire pantheon and my homebrew pantheons were built to align with the motivation of humanoids and intelligent monsters in older editions.
The Hells is an infinite expanse. At the Core is Asmodeus and his 9 Realms where the Devils reside. Surrounding his 9 Realms is the chaotic Abyss where the Demons lurk. Asmodeus is a fallen Angel that saw the potential of being too lawful (tyrannical), but found himself charged with protecting something at the Center of Hell from the Demonic Forces that instinctually are drawn there.
This is a much simpler cosmology and has served me well. I created it when I was young and didn't pay attention to the details and just made up stuff to fill in the cracks. It evolved a lot with 3E and the ideas of the Shadowfell, and I am about to reboot the entire thing for a new group of players. The only think I am going to change now are the Pantheons of the Gods to make them more accessible. I'm eliminating some of my own creations and replacing them with Greyhawk and Dawn War Gods with similar profiles.