Just pulling Command Demon out of your spellbook and putting it on your bars will do all that with the priorities you listed. Assuming you have auto self cast enabled in the Interface > Combat options.
As for the focus version.
#showtooltip
/cast [@focus,exists,nodead] [] Command Demon
If you want mouseover support.
#showtooltip
/cast [@mouseover,exists,nodead] [] Command Demon
If you wanna go fancy