Secondly, the installation process on my end requires explanation.
I have a Lenovo Ideapad Flex 2-15 (Intel i5-4210U, HD 4400, 12 GB RAM) and I am installing on 128GB USB. Initially, I was attempting to use APFS on the USB and install High Sierra. However, APFS was meant to be used with SSD rather than USB or HDD (having read multiple posts about it)
The simple fix was to use HFS+ filesystem on the USB and the installation was successful, albeit one restart - as per the guide.
ATH9KFixup (with bootargs: -ath9565) as well as VoodooHDA (Latest) were used to resolve WiFi (AR9565) and Audio issues.
Final thoughts, Bluetooth is not working -used Rehabman's BrcmPatchRAM2 & BrcmFirmwareRepo kext unfortunately, it did not work. Bluetooth taskbar icon is present but there is no devices label when opened.
Broadcom WiFi/Bluetooth [Guide] WiFi and Bluetooth working out of box on macOS with Apple branded Broadcom BCM94360. Enables specific half mini and M.2 BCM94352 on macOS with methods described below. Credit: RehabMan This thread does not support: macOS/Continuity Atheros/Qualcomm...
So far, the OS is working fine, HDA blacks out every now and then. BT issue resolved would be wonderful.