Spell-making will be almost entirely done via XML in the ability editor. The vast majority of gameplay effects can be done in that one editor.
In some cases, you'll need to script some of the effects, like a mod for any other modern game. To do this, you'll need the trigger editor. Using the trigger editor, you'll have to pay attention to how you code it to make sure it's MUI, but given that the GUI will be able to handle local variables, it shouldn't be too much of a problem for most people anymore.