"Am I making this more complicated than it needs to be?" Yes. And, actually, no. Using RAID1 to copy your OS drive is more complicated than it needs to be. Clone the drive with a tool like Norton Ghost, Acronis True Image, or the free version of EASEUS Disk Copy. Then try out the new copy as the only disk in the PC and see if it boots.
I welcome constructive correction from the community on this next part.
Booting from a RAID array is not simple. It requires a special install procedure during which RAID drivers are loaded and the RAID array is built. Transfer the data from the Hitachi to the Raid 0 array - simple. Transferring the OS - not.
I find it preferable to boot from a non-RAID drive. Keep image backups of your OS disk (not just partition, disk, so you catch the MBR) on some other drive. If the OS drive fails, restore the backup. It's easier than dealing with RAID.
RAID0 for your system disk will make the system faster, but more quirky, vulnerable, and hard to recover. Unless you absolutely need two 1 TB volumes, why not put
- One WD drive with the OS and, if necessary, data partition one containing stuff that is rarely changed and not used that often. Or, more fun, a few Linux distros.
- One WD drive with a 500 GB partition for data
- One Hitachi drive with backups
Everyone has a different approach. If I wanted two 1 TB partitions, myself, I would go out and buy another 1 TB drive. And I actually like RAID. I have an 8-drive external RAID array that I mostly fiddle with and benchmark. But it's too picky for my system drive when I can afford the downtime to replace the drive, get my backup image from the other room, and restore my backup image. YMMV.