Formatting the 3TB HDD to GPT is correct to get access to all of it at once. When you install Windows, only have the target drive connected to the PC on an Intel SATA port, or Windows will put the boot partition on another drive. If that drive is removed, the PC won't boot.
What is the purpose of setting those CSM options? If you want to install Windows 8 in UEFI booting mode, set CSM to disabled, and you're done. Those other options are only useable after the OS is installed in UEFI booting mode.