If AI can handle all the planning, does that mean I no longer need to think?

No. Rather it means that your planning position doesn't really exist anymore. At least not in a form that would require a human.

Think about what? I would have imagined that thinking in broad strokes would be all that is left, with the AI implementing your thinking.

AI can handle the planning if precedents exist for what you need done. Since AI cannot think, it cannot do anything original though it can create Frankensteins from disparate pieces ("art"). You will need to do some thinking yourself if you need to do something original. Which brings up the question: is what you are doing worth doing if it is not original? Note: making money does not necessarily require originality.