About splitting the of Japanese's god spirit, it's kind of explained in simple way by Reimu in one of the official manga It's about 3-4 pages including that linked page :)
In that case it’s more like spirits rather than fairiesNot the first timeAlthough the places, times, and methods were different, we have been in this worldWe have manifested in the pastAnd by the way, we can construct multiple identical equipments. Think of it like splitting of spiritIt's just that, although randomized, the soul will reside in vessel of a certain sizeThe soul of a ship doesn't just reside at the bottom of the sea. There are also places where we are being enshrinedSo we should be able to control the result to a certain degree by managing the composition of resources used
Ship construction recipeFairies also can't use power that doesn’t exist in their own ship. Accordingly, there's a limit to what I can build
Equipment limitation to certain ship classThat element also exists within us. We can't create equipment that doesn’t exist within usFor someone who just manifested herself for the first time, you sure know a lot
