Kiting in Brisbane during winter is not usually that fantastic, but the odd day can come in. The water isn't super cold (spanner water) but a wet suite would help for the very chilly days. I don't usually worry about one but, you'll be more comfortable with at least a 3/4, 3mm. The wind will be mostly westerly/offshore, if anything at all, so you'll be limited to the amount of spots you can go too. I think you can kite at Wellington Point in a westerly, but I never have. At Scarborough, next to the Marina, is a beach that you can kite in a N/W which goes alright. Pelican Park at Clontarf, I hear can be done as well. There's bound to be few days over winter, but it's usually no where near as windy, and as often.