This theme of longing runs through the whole series. Caspian's longing for the old days to return in PC, Reepicheep's longing for Aslan's Country (his heart's desire), Digory's hope of finding a cure for his mother in another world, the entire third act of The Last Battle...

Very good point.
Longing was a recurring theme through much of Lewis' life as well. He felt a longing towards something he didn't quite know what was - he sometimes spoke of it as joy, sometimes talked about northernness ... It was something he could feel as a pang at times, but only something to slip from his grasp and still have to be longed for. His biography Surprised by Joy tells about his way towards finding its true source.

Courage might be one of the themes of the book.

Yes, definitely. Not forgetting that Corin dragged Shasta into fighting in a battle he never expected to be in and was untrained to participate in. At least he could ride the horse. Let us also not forget Lucy the Valiant, riding to the relief of Anvard as well as King Edmund the Just. And King Lune outlining what is expected of a king and a leader, who does his duty. How a king has no more leave to start away from his post than the lowliest soldier.

What about the other three classical virtues of Prudence, Temperance and Justice? How would they fit in HHB?

What about the other three classical virtues of Prudence, Temperance and Justice? How would they fit in HHB?

What about Rabadash when he said "I shall exercise prudence and courtesy and spill as little Narnian blood as I can."