I've got the same laptop (FX503VD) but not on the High Sierra (macOS Mojave 10.14.3 installed). I have followed this excellent guide and got it almost all working (still waiting for the Wi-Fi/BT card to arrive though).
The only thing that I'm struggling to achieve is the Sleep/Wake function. I've searched everywhere I could, tried tons of Clover options combinations, did various DSDT patches, (of course) ejected all USB devices, made custom SSDT for USB ports, tried various BIOS settings, etc
When the system goes to sleep, it wakes up immediately after 2 seconds.
That's what syslog says:
localhost kernel[0]: (AppleACPIPlatform) AppleACPIPlatformPower Wake reason: RTC XHC (Alarm)
SOLVED: Updated BIOS from v302 > v305, reassembled DSDT.aml and the problem is gone
Now besides the DGPU & PCIE Card Reader, everything else is fully functional, including battery state & trackpad (which was a big problem for me until I found this guide)