Dont go over 23kg - there is a small little note that says over-23-kg may need to be shipped, which wont happen for luggage but may happen for gear. Which is probably a bad thing.
When they ask "what is in it?", just tell the truth... "surf gear".

I'd also suggest, dont scrimp on purchased-baggage... give yourself every reason to be confident that they aren't going to query anything, which just drives up stress levels just at the time where you dont have an option to leave gear sitting in the airport.