But there are 3 Walkers, and 4 Horsemen? I do kind of like the idea but don't know how it would fit.
Pestilence - Nemesis
War - He Who Walks Before
Death - He Who Walks Behind
Famine - ??
That's a misnomer everyone believes because three beer bottles were placed side by side... but no evidence exists this claim is true... and syntax would actually indicate otherwise per SF. "Those who walk before and he who walks behind"
I'd actually break it down
He Who Walks Before=Fearbringer
He Who Walks Before=Despair
He Who Walks Before=Lust(keeping in mind this is inclusive of the idea of greed and other forms of desire)
The End Walks the Land.... aka Mother Winter.
He Who Walks Behind=Death.
Which I know, doesn't include Nemesis, but I don't think N is a simple Walker, and if She is, it's likely a permutation of The End i'm not thinking of, though her aspect tends to be The Chooser not The End.
With any permutations of such being simply the mask of their power they managed to fit into reality al la pestilence, Famine, ect. I think also that previous masks have already been repurposed under new identity in reality to new hosts... With for instance, EK being a decent 'Beasts' while the Archive would closely suit human 'Conquest'.(oh hey and look, they tried to off or corrupt both those guys at one point or another, DB eating EK in the Hollow, SmF getting Ivy a coin, a Nemfected/traitorous coin likely at that)
Technically by the wording of the book, I have more evidence in my favor than 'the 3 Walkers'(especially Beside... though I think he may have added Those Who Walk Beside as a specific turn of in house joke in response to an idea based on people erroraniously thinking the 3rd Walker is Beside, he made Odin and his ilk the 'Beside' humanity guys) we just know 3 are coming for Harry, not any defined # or totality.