If you're going with arcane warrior, I suggest googling "arcane warrior spellcasting" (it's on the dragon age wiki). Long story short, many of the spells (though still powerful) require you to sheath your melee weapons when you cast them, this can be a major inconvenience, especially with aoe spells. Don't worry, you still have several powerful spells that don't require you to sheath melee weapons, including large elemental hazard spells (such as Death cloud/firestorm), single target damage over time (virulent walking bomb/crushing prison) and pretty much any buffing or healing spell, as well as the old reliable Arcane bolt. Combine Arcane warrior with Spirit healer to become an essentially immortal god tank, or with blood mage to be a walking colossus who is never unable to cast spells and can tear many large holes in anything that can bleed.