If you are willing to take suggestions and if you want to keep the magic system in place. Keep it a generalized magic system like most others have it. The heat based magic is a good idea but it doesn't leave much to creativity. Another suggestion for the magic make it dangerous to the user and at the same time making it a watched over and regulated skill. Like the more you user or if you are a unskilled user the higher chance you become a a pawn of the discarded like the potential "daemons". It could also give you something to add to the cult. ie they are using unregulated magic in order to become closer to the discarded.

[@Pezz570]