And I'm sorry, I might have missed the answer to this... Is it standalone and self-contained? Or is it like M&M/W&W where it's more a fantasy supplement for Spycraft than a standalone game?
-O
As Foghorn said, it's stand alone. You might want the Spellbound PDFs for 'specialist' mages, Fragile Minds for CoC style horror (namely the Table of Sproing, the stress damage version of the critical injury table), and Origin of the Species: Lights of Olympus for PC Centaurs, Fauns, Merfolk, and Medusas. Origin of the Species: Classic Fantasy will help if you want more subraces for Elves, Dwarves, and Pech, or Half-Elven and Half-Orc PCs. Using these might take some extra work though, since they're written for Spycraft 2.0. About as much as, say 3.0 to 3.5 or 3.5 to Pathfinder, but not always as obvious.
That said, the Mage is perfectly servicable as the sole spellcaster, Stress Damage will serve your needs if you don't want insanity to be a risk the way it is in CoC, and the book has rules for Dragon, Dwarf, Elf, Giant, Goblin, Human, Ogre, Orc, Pech (Halflings), Treant, Lizardman, and Unborn (Warforged, Golmens, Clockwork Men, etc) PCs.