I run mine headless and no problems rebooting it headless and managing it using Screen Sharing. I have nothing plugged into the display port.
I set it up to auto login to the main account with admin access. I use the Roon server which has no user interface and set it to launch at startup. I also set HQPlayer to startup automatically.
Here are Energy Saver settings:
Also, I issue this terminal command:
sudo pmset -a disksleep 1410065408
It keeps the disks from sleeping…even the SSD I assume.