Although I'm not intimately familiar with your car, normal would be to fill the radiator to the top with a 50-50 coolant mixture suitable for the radiator material (bronze, aluminum, etc) and let the coolant find its own level. That's assuming that you have a radiator overflow and return pressure cap (whatever pressure is suitable for your car's system) - and the overflowing coolant is led to a catch container with its own overflow hose. With the proper cap, the radiator will always be full - expanded hot coolant will be led to the overflow tank, and when the system cools down, coolant will be sucked back into the system.