I also did hapkido as part of my TKD training (~ 4 years) up through asst. Black belt. My Instructor was Grandmaster Chung, Sang Chel in Chicago. As far as internal training, we did some ChiGung like exercises, that GM Chung indicated were good for your health and improved your strength, but we did not do them every practice. The throws we practiced were more akin to judo throws, but there were some hosinsool techniques (grab defenses mostly) that were similar to aikido techniques combined with strong atemi. The application was not at all like the USAF aikido I've practiced more recently, or the DR Roppokai techniques I saw Popkin Sensei do in a recent seminar.
All that aside, HKD is a fun and practical art, and I enjoyed my practice immensely. Demonstrations had a tendancy toward the theatrical, a practice which was encouraged as part of the art by my recollection. I'd probably still be with GM Chung if I hadn't moved out west.