Dell OptiPlex 9010 external RAID support

Hello,

I have an old Dell OptiPlex 9010 Mini CPU tower which I am planning to convert to a home NAS by adding an external PCIe x2 RAID card. My questions are:

1. As per its user manual this model supports maximum of 1 TB HDD. Is this limited on board RAID and can I get around it by adding an external RAID card? I am planning to add 4x 4TB HDD with RAID10 config.

2. I have a StarTech 6gbps RAID card x2 PCIe. When I install it to Slot 1 PCIe (with no HDD connected) the BIOS identify it as "external mass storage" and everything works fine however when I connect a 1 TB HDD to it and boot, I get "Error Type 6" and even though the system boots up, I don't see the attached HDD.