Moving, casting, and targeting. ASD keys uses 1 hand. Arrow keys uses 1 hand. Mouse uses 1 hand. That is 3 hands unless you decide to break from old habits and use the num pad.
Spells are useless even when targeting other players because they have like 3 seconds to dodge them because spells are SLOW.
Anyway... can you instead make it so it it targets when you hold A while S casting instead of A to not target cast?