If you are using a system with no IGPU then iMacPro1,1 or Mac Pro 7,1 are better options than the Coffee Lake (CFL) iMac you are using. As the iMac19,1 expects an IGPU to be present even if it is running Headless, i.e. with an empty framebuffer.
You need to add SSDT-PLUG.aml to your /OC/APCI folder, for CPU power management.
As you are using a Z370 board you do not need SSDT-PMC.aml.
You need to add USBInjectAll.kext to your /OC/Kexts folder for USB configuration/setup.
Your /OC/Drivers folder contains a lot of useless and unnecessary entries. All you need is HfsPlus.efi and OpenRuntime.efi. You should only add OpenCanopy.efi if you are booting with the OC GUI instead of the picker list. The rest can be deleted as you don't need them to boot your CFL system.