When I do my shadow priests, I usually have isboxer spamm 4 buttons for me. 3 of the buttons are just cooldown based abilities. These are Mind blast, Halo and Shadow word eath. The 4th button is a cast sequence macro that contains Shadow word: Pain, Vampiric touch and Mind flay. I manually add Devouring Plague when I see them having 3 orbs on them.
The healing part I dont add in my spamm buttons, I use an healing addon for the healer with isboxers video fx to be shown on the tanks window so I can easily heal if needed and not waste it.