If you select Gigabyte motherboard, they have pretty good model for 6 GPU. and it has slot for m.2 SSD so your rig will look better because you dont have to stretch two cables (sata power and data) to classical SSD. M.2 is directly on the board.
Also I would definitely recommend MSI Nvidia GTX 1060, it is much cheaper than 1070 and you can easily get 23.5 Mh/s on ethereum with right overclock by MSI afterburner.