FaceTime and Messages etc, require a working Apple iCloud account.
Apple's iCloud requires a working SMBIOS data set, which you can generate as detailed above. Don't be lazy, generate your own SMBIOS data set.
I don't understand why your graphics card is not showing correctly in About this Mac and the System Information > Graphics/Displays report. Your motherboard only has the one x16 PCIe slot, so it is not likely to be an issue with the PCIe slot you are using, your bios shows the AMD Integrated GFX is disabled and Initial graphics as the PCIe slot, you have Lilu.kext and WhateverGreen.kext in your OC/Kexts folder and both kexts are enabled in your config.plist.
While the GPU and display details are not shown in About this Mac and the system information report, this does not prevent your AMD GPU from working. I assume you can set your display to show the best resolution it supports, whether that is 1920x1080 or larger.
I can only assume the issue is related to the display connector and framebuffer the AMD GPU is using. To see if this is the case you would need to provide a copy of your IOReg.
How to Make a Copy of IOReg (Note 1)
1. IORegistryExplorer/File/Save a Copy As…. (no extension required)
2. Open file to verify (Note 2)
3. Attach to post (Note 3)
Installation
1, Open Downloads/IORegistryExplorer-SLRID_v10.6.3
2. Drag IORegistryExplorer to Applications
Notes
1. An IOReg.txt is not useful. It is not a "Copy of IOReg." Do not attach .txt files.
2. IOReg must open the file. If TextEdit opens, See Note 1.
3. Compress it (Finder/Compress ... )
Use the version of IORegistryExplorer below. Newer versions tend to corrupt the IOReg and make them unreadable.