I think so. I'm no expert with bows etc, but I would imagine that someone who
Another thing to consider with the walls: will people standing on the battlements on top of a 10 level tower (300ft. above the ground, you say) be able to accurately hit an attacker with any weapon in their possession? Otherwise, I'd say it's a waste to deploy troops there in the event of a ground attack. Of course, if there's a danger of aerial attacks, sure, go ahead.
I'd rather keep the overall shape of the building, even if it means raising the courtyard to the sixth level, or something.
Or maybe make the courtyard wall lower, the front towers lower as well, and add side-mounted towers (towers that don't go all the way to the ground) to the main building on the higher levels?