You should be able to work just fine in the config you’ve discovered. The only thing is you didn’t need to turn on the RAID capabilities. You could have just had it attached as dumb storage, individual drives, and partitioned them in Disk Management.
Don’t waist your money on a “RAID” card. There’s no advantage in having a hardware RAID-0 over Windows Disk Management striping. Just buy a quality SATA controller with 4 ports and create equal stripe sets that are no more than 200GB. For this type application I’d only buy a SATA RAID controller if I were going to run with RAID-3 or RAID-5.