If my cholesterol, and blood sugars and echocardiogram all are looking good, could I still have atherosclerosis? Any tests to determine if I do?

Probably not . It would be highly unusual for a 24 year old to have significant atherosclerosis. Other tests would include vascular ultrasound and stress tests.
Yes and yes. Almost all of us have some degree of hardening of the arteries, more as we age. If you have no symptoms, you probably need no further testing. Last year a friend was sold a "coronary calcium score" test. It was borderline high so he had a catherization which showed insignificant disease--but he almost died from a complication. You need tests when you have symptoms.