Hi Charlotte
Windsurfing and kitesurfing is a bit of a dead duck in the Whitsundays as the winds are offshore (Airlie Beach), You have to drive a long way to get to a windsurfable spot.
The Whitsunday sailing club offers free sailing tuition so there is no avenue for earning a living by charging for teaching sailing. You could try one of the many sailing charter companies who charter old racing maxi yachts for one to three days, (They dont pay much) .
Same goes for Cairns.
These companies are all experiencing downturns due to GFC and Aussie dollar going through the roof so there is high unemployment in this area .
Good luck