The CPU usually is not all that important in mining builds because most mining is completely GPU dependent and does not stress\use the CPU at all. I have not done it myself, but I read a few guides saying that they pair a decent Z270 board ( mostly for the PCIE ports and stability for power multiple GPU's), and cheap compatible processors, which in this case would be Intel's Pentium lineup. Here's a link to Newegg's page for it, https://www.newegg.com/Product/Product.aspx?item=N82E16819117625.
I don't really know which would the best to pick within the family, but logic says to pick the cheapest one. If you are only going to be using one GPU you can probably get a cheaper MB, but that may limit future plans to hook up more GPU's if you do.
Best of luck and have fun with it.