max supported gpu for win is 8 gpu if im not mistaken, anything more than 8 go linux.
WRONG
to set up any rig with 12 gpu its easy with the right motherboard , you must to have 6 nvidia and 6 AMD cards , this way the 12 cards setup under widows can not be a problem , really easy to set up . if you want 16 cards it is still possible under windows (10) but might be PITA (pain in the ass) to set up , but once the right configuration is set , you are ready to go
i have both 12 cards setup and 16 cards setup running without any problem under win 10 enterprise edition amd cards are with custom bios , latest blockchain driver , driver patch , nvidia cards overclocked/ undervolted with software