Does low cholesterol prevent atherosclerosis? If I have good cholesterol, meaning high good cholesterol and low bad cholesterol, will that prevent atherosclerosis?

Possibly. Atherosclerosis is caused by a variety of factors, of which cholesterol and triglycerides are two major components. Therefore, if you have low total cholesterol and an appropriate balance between LDL and hdl, you should reduce your risk substantially. But, you may still have development of atherosclerosis later in life. Still, here less is more :).
Having. Having good cholesterol goes a long way toward preventing atherosclerosis, but it is only one of several risk factors. Some risk factors cannot be controlled, such as your age, gender or family history. But other things you can do to help prevent atherosclerosis include never smoke tobacco or quit if you already do, achieve ideal blood pressure (less than 120/80), maintain a healthy body weight and participate in aerobic activity for at least 30 minutes 5 times a week.