So... I had 90% of this all typed up and I had totally intended to post it weeks ago but I forgot...
Oops. On the bright side, it did give me a chance to flesh it out a bit more and refine what I had some.
Just a bit of a disclaimer here, I can and will change any or all of this if the plot requires it. It shouldn't but I know myself well enough to put this here. Enjoy.
First, allow me to say that the Kislevites are not wrong in that there are a multitude of lesser spirits. Belief creates in warhammer and gods and spirits are things that people constantly turn to. In this, mages can make use of this belief to bring forth spirits of elements and the eight winds of magic that I shall call Elementals.
As an aside, spirits, gods, and such things reside in the astral plane which is sort of the warp but not really, the Realm of Chaos is a pocket dimension in it but is generally contained outside of the random daemon attacks that happen from time to time. The other gods have their own pocket dimensions in it as well and the ones that share a pantheon are typically interconnected or even partially merged together where they go from being a lone cabin in the woods and change into a gated community.
As spirits, elementals have a form of pseudo soul that allows them to produce magical energy ex nihilo but often just taking form takes quite a bit of energy so typically spirits use their magic to breach into the physical world to work their curses and blessings. Once bound into a physical object by a mage, they no longer have to spend a significant portion of their power just breaching into reality and thus why they are able to do so much more in reality than when they were in the astral planes.
The Elementals/Djinn of Araby are naturally appearing spirits shaped by the beliefs of the Araby people and strong mono element magic pooling in one spot that allows the spirit to take form. They are far more intelligent than most elementals because they also act as the Arabyian gods and are both shaped and empowered by that belief. This grants binders of Djinn a greater amount of power than binders of most other spirits as the religion shaped around them grants enhanced energy production and intelligence but at the cost of their binders needing to either make deals with them or somehow beat them into submission every time the binders have need of them.
The objects a mage uses to bind them will eventually fail after several decades of use which means creating another one and binding a new elemental inside of it or transferring the old elemental to a new bottle before it fails. Please note that a mage can only have one Elemental at a time and once a wind/element is chosen, they must stick to it or else. Elemental Spirits are all extremely possessive of their binder who, in their minds, are their champions/head priest (amusingly, kind of like cats in a way) and will fight constantly if a mage tries to bind multiple, causing the death of the binder or the loss of one or both elementals.
The sticking to one element/wind rule is because not only the rules about not mixing winds still apply, but also Elementals can sense the use of other winds/elements and will react like a yandere catching their beloved in bed with another woman/man(or women/men) and will single mindedly try to kill them.
An elemental can be banished from the physical world via the normal spells but instead of their soul going back across the boundary, they instead are sent back to their container and are able to reform there with a full day's rest. During which, any magical energy their binder could use is instead consumed and put to use reforming, making the method of using them as meatshields a curse and a blessing for a mage as their easy magic is now unavailable if they are dispelled and they still have a enemy to face but it also means having an expendable ally capable of either flinging damaging spells or physically battling it out with others.
Elementals act sort of like self powering Harry Potter wands, granting far safer and more controlled magic that is also easier to use along with an instant ally. At the cost of being vulnerable to being destroyed temporarily or permanently, potentially becoming a crutch, limited output which means long wait times if only using elemental generated magic, and being very hard to craft.
When I later speak of how easy or hard they are to bring forth, I mean in comparison. Even an elemental of fire requires at least three experienced and skilled mages to call forth and bind properly. Controlling one requires a skilled/experienced mage who isn't casting anything more than low level spells at the most to actually control it, ones like Heavens(lightning) elementals typically require all of the focus a mage has so as not to have rogue lightning going around and zapping friend and foe without restraint.
When I say control, I mean ordering the elementals around when you let the "genie" out of the bottle and take "physical" form. If they are Elementals of the Lore of Fire then unleashing them from their container and using them in battle or everyday life would be very hard as they need constant management from their binder so as to prevent them from going wild. But an Metal Elemental would be like ordering around a robot, one that is only capable of following commands like: Follow, stay, attack, stop, etc.
In the distant future, as the skill and knowledge of the average mage improves and spreads, they will eventually (I'm talking 60 to 300 years here) be able to grant elementals in a bottle to every journeyman mage like they were starter pokemon albeit ones they can only release from their pokeballs if they and everyone else was going to die anyways. It would still require 2-3 master level mages helping out and reaching journeyman level before the age of 22 would be a notable feat, but it is still something that will happen in the distant future.
Elementals of the Lore of Fire are naturally made of fire. Easy to bring forth but always testing the control of the binder.
Elementals of the Lore of Heavens can be made up of air or lightning, air being far easier to control and bring forth than lightning but lightning is far stronger and powerful but are incredibly taxing to both bring forth and control.
Elementals of the Lore of Metal are made of metal, resembling statues of various creatures and while more difficult to bring forth than most, they are very easy to control once done.
Elementals of the Lore of Beasts are shapeshifters who take the form of various animals at random or on their binder's orders. They take some skill to tame but once done, they are usually not that hard to work with, some would even say a delight. Some are crazy animal whisperers.
Elementals of the Lore of Life can be made up of water, earth, or plants. Fenbeasts can be considered empowered versions that gain their power at the cost of needing constant upkeep beyond what they can produce to maintain their existence. Elementals of Life are the dead middle of elementals to bring forth and control.
Elementals of the Lore of Light look like small tinkerbell style fairies of light. These are the most difficult to bring forth and control over them is somewhat difficult.
Elementals of the Lore of Death are ethereal ravens, as if they were the ghost of one. These are paradoxically one of the hardest and easiest to bring forth, depending on whether or not you are doing in an area with lots (I mean hundreds at least) of recent death or not. Control is difficult.
Elementals of the Lore of Shadows are most often a blurry shadow figure, as if a man made of shadows. The easiest to bring forth as long as you do it during twilight. Generally not hard in difficulty to control but will sometimes decide to test their binder in their control over them.
In comparison to each other in how difficult they are to bring forth from hardest to easiest it would go like this: Light, Heavens(lightning), Death(no recent deaths nearby), Metal, Beasts, Life, Heavens(air), Shadow(not twilight), Fire, Death(recent deaths nearby), Shadow(twilight).
While Control in order of hardest to easiest would go something like this: Heavens(lightning), Fire, Death, Shadow(testing), Light, Life, Heavens(air)/Beasts (tied), Shadow(not testing), Metal.
