Marfan syndrome. It sounds like you suspect you may have marfan. Your doctor will address your concerns, and conduct a workup based on his evaluation. Aortic aneurysm is indeed something to be concerned about in these patients. I compliment you on your research. Echocardiogram, ct are relatively low risk for the diagnostic benefit and early fix, so if your doc recommended them, i'd strongly consider.
Not necessarily. The body habitus described is often typical of patients who have pectus excavatum deformities, as well as with an inherited connective tissue disorder such as marfan's syndrome, where aneurysms would be a risk, more information is necessary. Are there any other associated signs such as hyperextended joints, high arched palate, lens subluxation, etc. A good exam and cxr could be helpful to start.