Is admiring a young man because of his morals and good looks, in the context of following his da'wah and educational work, considered forbidden?

Your admiration for this man's handsomeness is not forbidden, as long as it does not lead to something forbidden or deviate from the natural disposition and upright conduct. The اصل (fundamental principle) is that your love and admiration for him should be for the good and righteousness he possesses, so strive to achieve that. And know that the unrestrained surge of emotions, whether love or hatred, if it exceeds the limit, is blameworthy, while moderation and balance are praised in Islamic law.