Hi tejhatjhte,
I am Dave, an Independent Advisor, I will help you with this . . .
Windows 10 has functionality named Storage Spaces, which is the best way to implement Raid from inside Windows 10, you can read about that on this page:
https://support.microsoft.com/en-us/windows/sto...
If you want to set up Raid in BIOS, then you would need to re-install Windows 10, and with regards to having to buy Windows 10, you do not need to do that, you can create a bootable Windows 10 USB anytime, it is free to do so:
Click this link:
https://www.microsoft.com/en-us/software-downlo...
to download the Media Creation Tool (Click on Download Tool Now), with that you can download the latest Windows 10 ISO (Select Create Installation Media for Another PC), you can create a bootable USB flash drive (min 8GB) using that tool