It really depends on the natural thickness of your lashes, people with pale or thin or short lashes can need up to as many as 6 coats to get really good definition and coverage, where as others only need 1 or 2!
Coats depend on how thick your lashes are. I have short and thin lashes, but when curled, I only use one. Too many coats can make the mascara clumpy. I think max would be three, but make sure you brush out your lashes after.