My first reaction is that (as others have indicated) it doesn't seem right that some wizards should be subject to automatic, free compels. If Harry walks into Murphy's office and blows up her computer, then that is a complication and he deserves Fate for it. Note that if a wizard accidentally blows out the radio in a passing car but it doesn't actually complicate the wizard's life in any meaningful way, then that's just fluff and doesn't deserve a Fate point.
As to the remaining mechanics, I see value in creating such mechanics (as guidelines, if not hard/fast rules), but I have doubts about the specific ones you suggest. For example, it seems as though Discipline should be a key factor (in making hexing less likely) rather than Conviction playing a role in making it more likely.
So perhaps my take on the mechanics would look more like this:
* First, create a mechanic to 'measure' emotional stress. For lack of a better term, I'll use "emotion points" for now.
* The player gains emotion points whenever it seems appropriate. Examples of triggers might include: taking a consequence, either invoking an emotion-based aspect or having it evoked/compelled by others (ie, Harry's "Still Quick to Anger", or similar temporary aspects), being subject to Incite Emotion (or having your emotions manipulated mundanely), suffering a failure of some significance, or any number of other options.
* Any time the wizard gains an emotion point or casts a spell, there's an opportunity for accidental hexing, the GM chooses whether or not this occurs. If it does, the player makes a Discipline roll against the number of emotion points he's accumulated. Failure means an accidental hex based on the shifts by which the roll failed. (Note that this still counts as a compel, complete with a Fate point.) Success means no hex, and the wizard discards one emotion point due to successfully controlling his emotions.
* The wizard can make a deliberate attempt to reduce emotion points by engaging in some form of relaxation. Make a Discipline roll (against emotion points) after a full scene of uninterrupted relaxation, and reduce emotion points by the number of shifts earned. Even if the roll fails, the wizard discards one emotion point regardless.
I guess this ends up kind of looking a bit like the Hunger rules. And of course I've not playtested it in any way (or even though about it all that much), so I might be missing something important.