G'day Guy77,
Given your time in... don't even bother packing your 20m if you weigh anything less than about 500kg and ride anything bigger than an icy-pole stick... seriously! (Mine is soundly packed away for the winter, icy-pole stick included.)
Bring your 13m and as much skill as you can muster.
StKilda is going to leave you very limited in possibilities, and the water will be filthy. The northerlies have set in and you will need to travel. Buddy up with one/some of the locals. Breeze by
www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=15414 to get a feel for the local kite-nuts. (Just watch out for Audi driving bow-kiters; some of them are notoriously nice fellas, that are more than happy to see another smiling dial on a kitable beach.)