CPU for WoW
What is the most important things to look for when buying a CPU for WoW, what does the game need to operate at its max level: Cores, Threads, Frequency speed (GHz), cache, bus speed?????
For best results, all of the above.
More seriously though, pretty much any mid-range quad core and up will do. Ryzen 3, Ryzen 5, Core i3 8th gen and up. Blizzard has spent a little time on their old engine and have recently added more multi-threaded support, so you are no longer looking for the fastest single core speed, though it certainly doesn't hurt. Still a very CPU heavy title.
Graphics wise you don't need a whole lot. Any discrete GPU will be adequate, though for maximum results at 1080p you want to look at GTX1050Ti or RX560/570 territory. There are a few areas that are quite high in polygon counts, and dungeons and raiding have a lot of effects on the screen at once. All this is settings driven though, you can sacrifice things like shadows and volumetric lighting. They've also added different settings for overworld play vs dungeons and raids, which makes it quite convenient to have two graphics profiles.
An Intel 8th or 9th gen i5 would be an excellent choice, but due to horrible Intel pricing, due to low supply, I would say an R5 2600 is the sweet spot, for price/performance. The problem with WoW, as Bellular put it, "It runs on everything, but runs well on nothing". Most of this is due to its subpar multithreaded performance. That will hopefully be changing in a future patch, as it is known to be something Blizzard is working on.