I generally recommend having a single drive for the OS or a RAID1 for redundancy. From there you can build any sized RAID for your storage need. Even on the servers we build at work (used for evidence storage) uses a single drive setup for the OS and several drives for storage in RAID with hot spares in place. This keeps the data safe and ensures the OS cannot crap out and corrupt your important data. Windows has become more and more reliable over the years, but I still don't implicitly trust it.