Windows 10 is the choice. But its still not good. After every windows update you will run into some new stupid complication. If i were you i'd try to split up the cards on two rigs, keeping each rig either Nvidia or AMD. Your downtime with stupid problems would be cut in half. If not more.
Hmm I really don't know what I should do. Suppliers telling me there is a new gpu batch coming in March and my goal for 2018 would be to add 6-7 cards each quarter. So at the end of 2018 overall goal is 26 pgu cards. I already got lucky on two AS Rock 110 (210 dollar each) boards and thought it would be better longterm two maintain 2 systems (2x 13) instead of 4 (4x 6-7)? Anyway currently I "only" own 6 cards and start with windows but I'm not sure how I should progress and set up my "foundation" for the overall goal.