I have a rig on this MB, it wasn't easy to get it works, spend a lot of time, got a lot of experience
Initially MB refuses to load from USB, any type of storage flash drives, CD/DVD.
BIOS was starting normally, USB mouse worked and USB drives were seen in Boot menu and BIOS settings, but after initial booting from any kind of device USB stopped responding, nothing helped, tried change USB settings (Legacy in BIOS), different types of installation media USB sticks, USB CD/DVD, various OS (Win 7, Win 10, Linux). Unfortunately don't have any SATA DVD Reader to install from.
And even when Windows 10 booted to first screen with language and keyboard selection I was unable to select anything, keyboard and mouses didn't work.
I found a few articles that there are problems with USB during OS installation on Intel chipsets. Friend give me PS/2 keyboard and I found PS/2 mouse.
What i did, install Windows 7 using rig's SSD on different PC, and then connected SSD to ASRock MB it started to work, then updated all drivers.
Next issue was - it refuses to running more then 6 cards, regardless of type Nvidia or AMD. That wasn't Power supply, risers or other connections issue, I tried to find solution for several days, but that was definitely software issue, Windows 10 installation resolve issue completely.
So I recommend to use Windows 10 64-bit with this MB or Linux.
Currently running 8x EVGA 1070 FTW/FTW2 + 1x Sapphire Radeon RX580 Nitro, waiting for PCI-E power cables to connect more cards.
Now next setup is working:
Windows 10 Pro 64bit
CPU - Celeron 3900
RAM - 2x 4Gb
MB - AsRock H100 Pro BTC+
SSD - Corsair Force LS 60Gb
PSU - 1x Corsair HX1200i + Corsair 1x HX1200
8x EVGA 1070 FTW/FTW2 + 1x Sapphire Radeon RX580 Nitro
If I will expand number of Nvidia cards will have to switch to Linux or buy Radeons only. Already tried nvOC on 1070 EVGA FTW card on my main desktop and liked it, spend some minutes to configure all in one file and you are ready. Just need to play with power and OC setting on live system for better results.