the castle does not really live up to your idea of being quite defensive, its walls are very low in large areas, it looks more like a fortified mansion than a castle, sitting on a very insignificant hill. having only layer of defense (gate), lacking towers in some places to oversee the entire perimeter of the castle walls, and lacking any sort of keep or burgfried. Lastly you kinda took only the chapel area of your inspiration and "converted" it into a castle, which is pretty much highlights the facts why your castle seems bit incomplete, lacking some key features and defensive measures, I also think you might struggle including key facilities in the interior of the castle ( like granary, armory, solider & servant accommodations, carpenter, smith etc...) unless you plan to create vast dungeon since from the outside right now it looks like that 90% of the buildings are allocated to the needs of the nobility with its balconies and other luxuries. remember a castle was made primarily for defense.It is not a grant house however it is located on a region border so its castle is quite defensive
You are telling us that this side of the wall will be 100% safe, because of the steepness of the slope, however if you are trying to make the slope steep, i am very worried that you will have a hard time making it look natural, since as you said, you will be blending the mound into the terrain around that castle, and it will look very awkward to have on 3 sides of the castle nice and smooth slope and on the 4th side a rapid slope.That’s why the nobility- yard is placed there because the ground beneath the walls is going to be very steep making them 100% safe.
It is true that it looks more than a fortified mansion rather than a castle. This is because I saw on the list of available projects that Rankenfell is of lesser importance but in my opinion it has to be fortified. Due to the fact that its status is “Lord (3)” in the post and the fact that there is almost nothing mentioned about it, I gathered that it is of lesser importance. Therefore the “mansion” I made is enough for the nobility to live there(with some extra buildings to match it) but due to the fact that it is located on a border and near a location that extracts gold (Goldentooth) with great importance, it has to be fortified.