If they're all Nvidia GPUs, I'd go ahead and use Ubuntu or your preferred Linux distribution.
Also, as xxcsu mentioned, if you use the Asus B250 mining expert, you cannot exceed 13 cards without having at least 6 P106 mining-specific cards. (Supposedly Asus has plans to remove that requirement, but we'll see.) However, this limitation is not specific to Windows.
The typical limit was 8 Nvidia GPUs, but that seems to have changed. Note that setup headaches often remain as you go higher.
For reference: https://bitcointalksearch.org/topic/8-card-limit-on-windows-is-removed-2302268