TSC,
Thanks for the questions.
(1) Ankylosing spondylitis (AS) has been associated with valvular heart disease, most specifically aortic regurgitation (AR). The literature available to me on a saturday was sparse. However, I have never had a patient referred to me with AS and AR.
(3) The classic hypermetabolic disorders affecting the heart would include hyperthyroidism, pheochromocytoma, beri-beri, AV fistulas, Paget's disease, and I'm sure a few others.
(4)Palpitations is the symptom of feeling one's heartbeat: it can be fast, slow, irregular, strong, hard, etc.
(5)While I can't make specific recommendations for your case without a full history and physical, I would be likely to look only for a sign of systemic illness, such as hyperthyroidism or one of the others mentioned, and then focus on treatment. Possible therapies will include bio-feedback and counseling.
(6) Costochondritis simply means "inflammation of the the rib joints". If you have costochondritis, it should raise the suspicion of AS. AS can cause shortness of breath via altered chest wall mechanics. It might also be changing the geometry of your chest, and thus leading to the heightened heart sensation.
Good Luck.