Queenstown, the lake is cold water.
Been there windsurfing in the past during summer and wore 4/3 steamer.
Sup you probably won't wear wetsuit (sweat suit) a pair of botties could be recommended. Any time of year you can get southerly change which can bring snow so bring thermals.
With the shape of the lake one arm can be glassy and another windy.
Its expensive place but amazing when you're on the water with the hills around

enjoy