QN90C and QN90B offer excellent picture quality, and great brightness. My preference leans towards the QN90C due to its IPS panels. However, if you find a good deal on the QN90B, it's still a solid choice.
To fix Windows activation error code 0xC004F213 you need to log in to your Microsoft account, try to enter the license key manually, use PowerShell to find out the key written into the motherboard or use the built-in activation error troubleshooting tool.