Generally, it works out like WoD stats multiplied by around 5 or 6. A normal-strength person has Muscle:10, a person who jogs a bit would have 15, someone actually 'strong' would have 20, human max is 30, rough inhuman max is about 50. Some of the funky powers work on a pure 1-to-1 ratio, like how Flying (vampire power. It's based on the Anita Blake books so some of them can do this 'Forever Knight' type flying thing) is how many miles per hour you can hover around at and can be directly added to your attack/defense if slamming into folks or zipping around. Others work on a scale where 1-10 has a range of things you can do, 11-20 has a range, et cetera..
When working up what sort've powers the Fae would have, I took a bit of a cue from WoD Mage and gave them departments of magic. Air Magic, Water Magic, Earth Magic, Fire Magic are all pretty obvious. Flesh Magic is pretty much WoD Mage Life, covering healing and shapechanging. Dream Magic is pretty much WoD Mage Mind, covering mind reading, telepathy, and general 'Jedi Mind Tricks'. Light Magic is illusions, Darkness Magic is shadows. To round it out, I tossed in Luck Magic which can be used to up just about anything (but if used to boost other departments of magic, the effects can be zapped by 'mythic things').
My problem stems in trying to define what these powers can do. So far I've dabbled around with this for an idea..
A branch of Fae Magics, Air Magic can be broken up into roughly four levels: Detection, Manipulation, Transmutation, and Creation.
Detection is pretty easy. For each level you have in it, you can detect changes up to a foot away from yourself. It's much like if you had a way to highlight the odd parts, so you might actually be able to detect a slight wisp of gas across the room, but you might not know it's gas. Air Magic can be added to Observation to try to identify something with your eyes, or Senses if you're just detecting it (like say, behind you).
For each 5 levels you have in Air Magic (rounded down), you can attempt Manipulation of one cubic foot per minute. This largely shoves the air around in gusts with a strength equal to your Air Magic. With Air Magic:10 you can push 2 cubic feet around with Muscle:10 for a minute, or 1 cubic foot with Muscle:10 for two minutes. If you can manipulate enough (if we imagine 1 Muscle can move 10 lbs), you can lift yourself or others off the ground.
For each 10 levels you have, you can attempt Transmutation (also one cubic foot per minute) from one gas to a similar gas. For each 15, you can attempt raw Creation.
..the other elemental ones pretty much are set up the same way. Trouble is, it seems a bit too clunky. I'm rather caught in between it being too clunky, or far too free-form (like that whole Transmutation thing? I'd like it so folks can easily do small little changes like water to wine, but it'd be nice if 'rain to hydrochloric acid' would be pretty tough).
Does anyone know of an established system that's close enough to this that it'd be easy enough to adapt to the needs here?