=========
I just got my Z370 Taichi - 8700K - Radeon RX580 kinda wrapped up last night. It now UEFI dual boots HS 10.13.3 and Windows 10 on separate Samsung M.2 500GB EVO's. I have tried darkwake=0 and darkwake=8. Both show the same issue as OP. The machine goes to sleep, then immediately comes back on and continues this cycle. It never 'reboots', so not sure if OP meant an actual reboot, or just comes back on.
Another interesting issue is that if you set sleep = never, it shuts down and does a BIOS B -> A copy. Reboots a couple more times then goes back to the Clover boot screen.
I have Ethernet, sound, and video working fine. 'About This Mac' reports the Radeon 580 8GB, and sees it as an iMac 27" Retina - 18,3. So far I am very happy with it and will continue to work out the sleep issue I hope. Of course the Intel wireless does not work. iMessage has alway been my achilles, haha.