I don't use facetime. I'd like to disable it so it doesn't automatically start following system startup. Is there a way to do this? (MacBook Pro, High Sierra)
Navigate to: System Preferences -> Users & Groups -> Login Items.
On this screen you can choose which programs will open automatically upon startup. You can remove FaceTime from this list to disable it opening on startup.
You can also add any programs you would actually like to start when you boot up.