OK my 2c worth.
Winter is not a good time to start learning. You will spend a lot of time in the water and being cold is not enjoyable, although now is a good time to get some gear together.
Depending on your budget you can either buy a complete board, sail, mast, boom package or hunt around and pick up individual items. Adelaide is not a very big market, if buying second hand, find some one that can look at the gear with you and give advice. Do not buy super old gear. The latest model of everything you can afford is best. You appear to have researched the type of board that would suit you, which is a start.
There is this board on the SA Buy and & Sell page : For Sale in Windsurfing - Boards $1,350 2013 JP Australia Fun Ride - 145 litres
Sail size to begin with, would depend on your fitness and ability to grasp the concept of windsurfing. A small size to begin with, then a larger one to suit your board once you have grasp the basics. ( Anywhere between 4.5m and 6.5m ).
Do not get a modern Cam sail, although the older style one's are ok as they have small mast pocket's. My personal view is that wave sails are good to learn on as they are very tough and forgiving. ( I have two old wave sails 4.7 and 5.4 and a 6.5m 3 Cam going cheap which I hope to put on Buy and sell shortly

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The next time there is some wind go for a trip to Boggy Lake and call into Strath Windsurf Shop on the way and have a chat with Gareth. Boggy would be one of the best places to learn. If down at Goolwa, there are a couple of regulars that sail on the lake, have a chat with them. You will find the windsurfing community a friendly bunch.