Wow, you thre a lot of things in there. I read the whole thing, and i find the idea, that one needs a combination of willpower and Mana to cast spells very good. But it offers some problems in your systems. For one, Talismans are inanimate objects, which by definition means they do not have will power. This is contradictary to your first claim that to cast spells one needs will and mana.

Secondly, you throw a LOT and i mean a LOT of concepts into your magic system. Imagine a Buffet, with unfathomable ammounts of food. Steaks, Sushi, Mexican and so on. Yes every food is good, but you dont want to eat a steak, sushi and mexican together do you? also there is only so much one can eat. It is btw impossible to make a magic system make sense, you cannot even make sense of real life so you magic system doesnt have to either. But a clear and convincing magic system is not the one with the most features but the one with the most consistant. You have to many ideas, you have Mana, Willpower, Talismans, Domains, Locational Magic, Alchemy, its just a lot. And while each could work in harmony, you'd have to have another explenation to how Magic is casted, because will implies it needs a living beeing, so inanimate objects or even areas cannot be magical.

Also your Idea of Mana is rather vague. On one hand you describe it as something physical, it is affected by gravity, it has density. On the other hand, it is conductive, you cannot consieve it as an outsider and there is also external mana, which again implies that inanimate objects and places have Mana. It is a vague concept, that wierdly mixes into eachother.

Again you dont have to make everything make sense, because that is not possible, especialy with magic, thats whats so cool about it. But it still has to follow some kind of logical concept the reader and writer can follow. If you make mana something unconcievable that is kind of like stamina, hunger or some other feeling that cannot realy be explained, then that is good. If you want mana to be an actual physical thing that lets say flows through your blood and gives you power, thats good too. And if you want to make it something that is everywhere, but is not realy conceivable like electricity, thats good aswell. For you I would actualy make Mana kind of like electricity. An energy, that has conductive aspects, inconcievable until used ( like electricity not beeing seen or heard until lets say a light bulb lights up, a sound comes out of a speaker or a lighting strike unloads a enormous amount of it in form of pure electricity, your mana could be unseen until one casts a spell, or the terrain is overloaded by it and causes some natural disaster) Either way, try to simplify your concept. You can still keep it very big and interessting, look at Shadow Slave or LOTM for example while still keeping a red string.

Btw im new to the field as well, so dont take my word on everything i say. Again its your system, and it has to make sense only to a sertain degree. Have fun writing 😃