Hi, your system looks nice, a good gpu and mobo.
If I were you I’d get a Blackmagic Ultrastudio SDI card or an Intensity card with USB3 interface, to output your image via HDMI or SDI to a grading monitor, which could be a good quality calibrated plasma display, Panasonic VT50 series for example. Or better still, a Sony OLED or some other reference monitor.
A GPU with 3-6 GB VRAM would also be great, especially if you’re working with larger than HD image sizes in the future. You may need a larger power supply with 2 GPU:s.