My general take on DV origins...
Before humans: Magic and the Nevernever probably originated at the same time as mortal life, billions of years ago, or possibly when animals developed brains or became complex enough to have emotions (we know animals have a 'metaphysical footprint', though a lesser one than humans, from DB - so presumably they influence the Nevernever as well, though less so than humans. No data on whether plants or microbes do. But given that T-rexes have a metaphysical footprint, the NN would have existed at least by dinosaur times.)
Simple animalistic fae might have existed. There was a lot of power around (the power of the Winter and Summer Queens is said to be "older than time" when Harry uses his Sight on them in SK, so presumably existed before humans) but it was undirected by consciousness - kind of a primeval chaos situation.
Human prehistory: With humans around, human emotions and thoughts shaped the Nevernever into more defined and complex forms. Minor fae started to manifest in human forms, like pixies. For some reason (bargains with humans like Lea does maybe?) some fae gained greater significance and power, and took on human-scale humanlike forms. These reproduced with humans and created changelings, some of whom then Chose Fae and became the parent-form of Fae directly rather than having to develop upwards from Little Folk (Meryl in SK became a troll). Either one or three powerful wizards performed a big sacrificial ascension ritual/spell with the stone table and became the first Faerie Queen(s). Other wizards performed similar rituals and became powerful Wyld Fae, the Erlking was one of these.
Unknown time: The Faerie Queens split between Summer and Winter.
About a thousand years ago: A major crisis in the supernatural power structure occurred. The Winter Queens took up the job of guarding the Outer Gates, and the Summer Queens became the guardians against Winter. This added purpose gave them greater power, but likely also even more constraints in how they could act in the mortal world. (This is possibly why the Winter and Summer Queens can't kill mortals, but Gwyn ap Nudd - a Wyld Fae lord - can.)