A simple 6-core should do fine.
Since you're planning to spend some money: With a Gigabyte Aorus GA-Z270X-Gaming 9, ASRock Z270 SuperCarrier or EVGA Z170 Classified 4-Way supporting min. 8x-PCIE on every slot you're also on the safe side. And they should cost less than that Asus X99E WS anyway.
Since you're planning to spend some money: With a Gigabyte Aorus GA-Z270X-Gaming 9, ASRock Z270 SuperCarrier or EVGA Z170 Classified 4-Way supporting min. 8x-PCIE on every slot you're also on the safe side. And they should cost less than that Asus X99E WS anyway.