Is it nessecary to have all the risk factors to be prone to have c.a.d, or one or two are enough to make someone prone to it?

Add up. Each risk factor for vascular disease "add together" to increase your overall risk for vascular disease. So if you smoke and have a family history and have an unfavorable cholesterol profile your risk of vascular disease is greater than if you only smoke and have a family history of vascular disease. Hope this helps, and again, know that every risk factor counts.
More risk factors. makes you higher risk, Less rid factors lowers your risk. They are Male sex Smoking, High BP, High Cholesterol, Family History of CAD, Sedentary life style, Dm, high CRP, Homocysteine level, and Post menopausal state( Lack of estrogen) Some of you can change; others you cannot by improving your life style.
No. You can have coronary artery disease without having any of the risk factors. Having them just increases the probability that you will at some time in your life have the disease.
Yes. Risk factors are population based which means in a large group of people those with more risk factors are more likely to develop CAD. The factors are identified by looking at people who have CAD and seeing what factors they have in common that are plausible causes of CAD. For any one individual you may or may not match the trend of the population. So you may be more or less susseptable/risk factor.