Hello everyone and its been quite a while!

Eventually I will be updating my main thread regarding my continents but for now I am struggling to get good references on the dimensions of a castle with a certain amount of realism. My questions are basically:
How wide would a keep be if we are talking of a massive castle?
What would be the best way to setup the space within (such as corridors and halls) without making it a labyrinth or an unpractical place to defend in times of war?