Down in Margs and the south coast during Autumn (March / April) the sea breezes aren't as strong and the LARGOS (late arvo glass off) can be a real killer. If you're kiting down that way, get out around 2 or 3 in the afternoon when there is a seabreeze, and by 4pm, be really careful as the seabreeze can just drop right out and it swings offshore. (sick for late arvo surf sessions though).
Exmouth / Geraldton etc is more likely to have a lot more consistent onshore winds than the SW / S coastline.
Lots of spots down on the southern margs coastline like Borranup and Conto's beaches (launch further north on Contos, not right in the corner in the wind shadow). North of Margs are lots of massive rocky headlands, narrow beaches and unforgving shallow reefs - steer clear unless you know the breaks really well and are comfortable kiting pretty serious size surf.
Kite size depends how much of a fat bastard you are!