plane creation help?

There is specific terminology around planar arrangements.
The 3.0e 'Planar Handbook' isn't the most widely known source for the D&D explanations, but it is quite detailed.
For your arrangement, I would consider whether the planes are: Separate Planes, Coterminous Planes, or Coexistent planes.

Separate Planes: Two planes that are separate do not overlap or directly connect to each other. They are like planets in different orbits. An outer Plane, for example, may have no direct connection with the Material Plane. The two planes are separate, and the only way to get form one plane to the other is to go through a third plane, such as the Astral Plane.

Coterminous Planes: Planes that link together at specific points are coterminous. Think of coterminous planes as touching each other. Where they touch, a connection exists and travelers can leave one reality behind and ether the other. The Astral Plane is coterminous plane to most other planes. is a coterminous plane to most other planes; it exists alongside them and can be accessed from them.

Coexistent Planes: If a link between two planes can be created at any point, the tow planes are coexistent.l These planes overlap each other completely. A coexistent plane can be reached from anywhere on the plane it overlaps. When moving a coexistent plane, it is often possible to see into or interact with the plane is coexists with The Ethereal Plane is coexistent with the Material Plane. Inhabitants of the Ethereal Plane can see into the Material Plane. Wit the right magic, inhabitants of the Material Plane can likewise see and interact with those on the Ethereal plane (see invisibility and magic missile, fore example, both affect the Ethereal Plane).

A Plane can be both coexistent and coterminous. The plane of Shadow, for example, is coexistent because it overlaps the Material Plane and can be accessed from there with the right spell or ability. But it's also coterminous-- it's possible to enter the Plane of Shadow at certain points, and travel to strange realms beyond the part of the plane that lies coexistent with the Material Plane.

The way you have currently described your arrangements, each transitional plane between the Domains is a demi-plane that is coexistent with both parent Domain planes. The demi-plane only exists where the two planes over lap. I diagrammed the 9-domain cosmology here:

You can assign the Domains by color, its arbitrary.

Where the planes overlap, you have your transitions. The planes can seem infinite, but they are actually 'smaller' than the pure Domain planes.
I find it interesting that, purely by the way I drew this, each of the domain planes is coexistent with the prime material plane (beige large circle) where they come near the edge of the plane. In-game, that would mean there are regions near the edge of reality where the Domain planes can be traveled to with a relatively low-level effect. It would be due to note that the pure Domain planes may not be hospitable to life, so those regions of overlap may be the only regions where PCs could travel.

It's also interesting that in my drawing above, the Prime Material plane is coterminous with each of the transition planes-- notice how each Domain plane overlap falls on a single point on the edge of the Prime Material Plane. This explains the "Halloween Town" in your system, where the entrance to the death-trickery realm is done through a single point on the edge of the Prime.
I think it would be illustrative to imagine a city, a valley, a maze or dungeon, some discrete point by which PCs could travel from the Prime Material Plane to these demi-Planes. It makes for convenient settings around which to run an adventure. It's also remarkable that to reach the ingress point to the demi-plane, you have to perfectly navigate the path between the Prime-Domain overlaps. That is, PCs would be able to tell they were getting close to Halloween town by perfectly avoiding the 'Trickery' and 'Death' portions of Domain coexistence. They shouldn't travel into either and the plane should reach an unavoidable point that is only Halloween Town, or to turn and return.

Planar reasoning is strange because so much of it works outside of 3-dimensions. The above diagram is just a projection of a cosmology in 2D. You can place the regions of overlap, the coterminous points in any point. This shows up all the time in-game setting because it makes everything extremely convenient, narratively. "Ley Lines" don't actually follow lines on the earth, to my understanding. They follow an interminable path in a manner beyond easy reason.

Anyway, this is my favorite exercise, making up demi-planes.

life/nature- A combination hive-greenhouse plane where plants & creatures small are perpetually being born and rushing off to the other planes. Spores, larvae, seeds, all sorts of natural and wild means of reproduction happen with abundance and randomness. Travelers must be wary lest their biology be incorporated involuntarily by the voracious growing locals.

nature/tempest- A massive jungle plane under constant spray, shower, wave & flood. The plane is constantly pounded by water of various droplet size & saturation from random and surprising directions. The core of the plane is the rotting decaying biomass knocked free or falling under weight of moss and molds, falling down to mulch the very plane. A perpetual mangrove of hurricane storms and constant damp that is escaped by climbing above the canopy.

tempest/war- An ongoing, infinite naval battle. The purgatory through which those who die in battle at sea must fight their way to the after life. The entire plane is ship after ship bound together by plank & hook, except those regions that are tempestuous storms, maelstroms, whirlpools, skerries covered in wrecks, etc. The combatants can not truly die, as there is no death in the particular plane. Instead, they battle and become more and more undead, more and more vengeful souls the further they are pushed to -HP. The only escape is to fight quickly through. Battling in this realm only makes the enemy into more potent forms of undead.

war/trickery- This curious plane exists in only a single room. The room is in a land beset by constant war amongst many factions. The room is neutral territory, where emissaries have agreed to meet to parley or determine terms. Those who enter the plane do not recognize their compatriots, and there are more present at the negotiation than just the PCs... All those who enter find a note in their effects as they sit to treaty. The note indicates that one or more around the table are traitors...

trickery/death- In this plane, those passing on may challenge death to any contest. The wages are life, or utter oblivion.

death/knowledge- Those deceased who find themselves in this plane are pressed into eternal accounting service. The throng of deceased who have talent in mathematics or organization enter a bureaucratic un-life. The work & labor of each are to determine some unknowable, incomprehensible truth or figure; the value of infinity or some other impossibly abstract truth. Only by completing their calculation can their endeavor end & they pass on. However, the determination of this meta-dimensional constant may destroy all reality in its conclusion.

knowledge/arcana- Library town. I wouldn't change a thing, but there needs to be golems. So many golems & constructs.

arcana/light- A transfer station. It's like an extraplanar operator board. Connections are made of all things, in all places. This includes the transfer of any intelligence from one place to another. Every teleportation would need to travel through these transfer boards, the cables connected by archons working quickly and diligently. It could also be the path by which new souls are put into bodies, new intellgences into creatures, constructs, intelligent items. Any number of opportunities for adventures from wires getting crossed and the wrong signal/person/message being sent to the right place.