Auto-starting on login will be a standard feature of RoonServer (the “headless” Roon Core).
However, we won;t run as a Windows service. That usually has annoyances related to SMB access, so you will need to setup your Mac/Windows machine to auto-login as a user.
That said, the RoonServer runs in the OS X menubar or the Windows System tray (that thing in the lower right), and from there you can quit or set the “Launch on Startup” option.