Do we need to book campsites in advance?
Is there a difference inlands and on the coast?
Well, I don't think you need to book in advance if you are prepared to be flexible about your accommodation: lets say you decide to stay in campsite A, but once you arrive there you realise that there is no space left so you go to campsite B. If you are not flexible then yes, you would have to make sure your camping plot is booked in advance.
sorry, i am not sure what you mean by "Is there a difference inlands and on the coast?"
Plese, can you be more specific?