Hi Frog, I love to see your work. its amazing and I can see you put so much effort and dedication into it. I have just started doing these homework myself. I think you nailed the Photoshop assignment as well the figure drawing one.
As for the Castle piece, I really like how you put all of them together. and I'd like to give couple of my thoughts.
First Scale: The proportion of the Human figures compared to the castle seemed to be bit off. I think you are trying to avoid to make them too small that they can be seen by the viewer so they can be used to convey the storytelling. But I think they should be a bit smaller, unless they are meant to be specifically bigger than Normal figures.
The Boat: I like how you crop the lights under the boat to add reflection effect on the water, I think you did a good job on this one. It would be nice to make the sail (cloth part) a bit convex to emphasize the wind blowing. This can be used to tell which direction the boat goes.
The Air Particle: I am seeing the Castle sort of "popped" from the rest of the object. The further the object from the camera the less saturated the color will be, its because there is layers of air particle this can be used to convey depth. Try to apply a bit into the boat as well so they feel like they belong in the environment.
The Shadows: So The sun is blocked by the Castle so there should be some shadows on the water. Also the Castle should look more like a silhouette shape since its against the light source (sun).
The Composition: As for the composition I think you can use rule of thirds and golden ratio to keep the composition interesting. Right now I see so much going on in the mid section of the picture. Meanwhile there is so much negative space on the right side of the picture. I think it would look better if you move the castle layer slightly to the right side of the image following the rule of thirds. Also shrink the Caslte size because right now the proportion between the Caslte and the Boat is almost 1 vs 1, it makes the viewer hard to determine which is the main focus and which is secondary one. As for the reference I think they are pretty good references. Overall I think you are pretty good in terms of the technique.
i like how you Blend the the old man's beard into the portrait and your Figure drawings are gorgeous. Keep it up !! I can see a lot potential in you.