Grand Australia & New Zealand trip Jan 20th

I am a single traveler, (widow, 75) and am booked on the Jan 20th trip Grand Australia and New Zealand. Would like to hear from other travelers on this trip. Also wondering about weather, and what to wear. Are shorts ok during the day? And will the nights still be cool? I understand black slacks and nice shirts will work for evenings, but wondering about how many layers we need and if shorts and capris are good day wear. I am from California, the Central Coast, and used to casual...I am there one night early to recover from jet lag, so will be in Melbourne one day before the tour starts.