Unable to open X display when launching Cinnamon

Your problem is the way you're starting Cinnamon.

When you type cinnamon, or gnome-shell, or gedit, or any other X app (a.k.a. X client), it tries to connect to an X server (started either by startx or a display manager). If it can't find one, it will fail. This is 100% expected.

You need to either startx or use a display manager to use Cinnamon. I've never heard of a desktop environment that starts the X server for you, except for XFCE (with startxfce).