as do i, now time for some math. argh blast you becq i get enough of this in my major >.>
There's not really much math, just add up the powers used, and done.
By the way, you might want to consider charging debt for the use of permanent demonic powers, too. I'm not sure how that balance would work out. But if you only pay two debt to get the Inhuman Strength permanently, and can use it forever 'for free', then there's much less reason to want a temporary power (which would cost the same two debt, but go away. I'm thinking one of the following options:
1) If you use any demonic powers in a scene, you get a point of debt (total).
2) If you use any demonic powers in a scene, you make a discipline or conviction roll (kind of like for hunger); if you fail you get a point of debt
3) If you use any demonic powers between milestones, you get a point of debt.
Any temporary powers don't count toward this, since you already paid for them (and will pay again if you want to use them later). The main point here is that if the character is really trying for that road of redemption, he not only needs to atone (by burning off the debt in a way that doesn't corrupt them utterly) but he also has to obstain from using his demonic powers, as well. And meanwhile, the FA will be goading him on, telling him that he and his friends wouldn't be suffering so much hardship if only he'd accept a
little help...
If you end up using any or all of the mechanics I've suggested, I'd love to hear feedback as to how it worked out and whether or not it 'felt' right.