My main is a mage, and I've actually setup Aura Frames to do pretty much exactly what you want with target debuffs. I use two containers. One is filtered to show my own debuffs and also anyone's Critical Mass or Shadow and Flame. The other is filtered to display the other debuffs. This gives ultimate display and layout flexibility (I use bars for the debuffs I really care about), and filtering is extremely cheap with this addon.
I use Weak Auras for the types of alerts you mention. That addon is excellent and very well suited for those sorts of tasks (and many more).