Tip for winter tips is to get a warm jacket, gloves, beanie, puffer vest, basically clothes that will make you warm. I went in summer as was so beautiful. I did 19 days in NZ was worth the value and baby steps yes I was nervous before the flight but flying with air new zealand made me more safe like I have traveled inter state before. You will be fine its not that far its 6 hours for you?
In queenstown go to Fergburger best burgers or devil burgers I was told were also good. Have you looked at contiki and topdeck or just topdeck?