Love the system. Is there a reason why WIS or CHA are not related with Theurgy/Witchcraft spell slot? Would it be okay to change it?
They are indeed used for that — WIS for theurgy, CHA for witchcraft — but that explanation is a little buried in a lengthy spell casting section near the end.
But also, of course you can change the rules to suit your purposes! I tried to explain in the design notes why I made certain design choices, but it’s quite normal to season to taste with D&Dish hacks like this.