Manual says 15 litres capacity. I guess the anti-freeze strength will depend on how balmy the winter evenings are round your area. I normally chuck in about 5lts (so about 33%) if I'm completelly refilling and I've never been frozen in sunny Scotland yet.
remember anti-freeze does more than lower the freezing point of the coolant. As someone who's just experienced a rotted out core plug, I'll never be cheap on the anti-freeze (bougt the car like that FWIW!)