With the southern oscillation index sitting on neutral (
www.bom.gov.au/climate/enso/ ) i'd say we're in for an ok but not brilliant summer. 12m for 83kg will be a decent size to start with - add a 9m as you begin to prioritise kiting in your finances

All the shops in Melbourne are reputable - sure, some prefer one over another and not everyone gets on well all the time but believe me, to stay afloat as a business in a market as small as kiting and related boardsports you need to take decent care of your customers. Shop around and get to know your options.
Give some thought (do some research) to 5 line vs 4 line. I prefer the simplicity of 4 lines myself. (As a beginner you'll probably put your kite through its lines fairly often and a 5th can complicate recovery from this.) Either way be sure to learn the safety and self-rescue process for whichever setup you choose.