Looks cool, but you may want to consider thickening the outer wall by double or triple. To me, it looks like a small band with pickaxes could get through the walls with little trouble. The dwarves would either have to come outside to stop them from breaking through or fight them where they break inside.

If you don't ant to make the walls thicker on the side rooms, you may consider raising them considerably. Like, 20 feet or so.