Hi @Gill, I would say Esperance has a cool Mediterranean climate; Esperance is usually a few degrees cooler than Perth. From the sounds of what you have said you should be fine with your honey reserves. However, I'm going to suggest that you consider packing your hive down to the brood box only for this first winter. I'd be surprised if your colony had sufficient numbers to get through a winter with a super on top if you only got the Nuc 3 months ago.
You could make this decision by monitoring the hive numbers and if the brood box looks less than about 70-80% full consider removing the super. Once you decide winter has arrived you shouldn't have a need to inspect your hive until the very start of spring, at which point you only add a super once your brood box appears about 80% full with bees.
Regarding your winter preparation, take a look through this forum for "leaking roof". That might be the main problem you encounter. I put aluminium flashing from Bunnings over my hive roof in winter to help address the problem.
And yes, if the frames are fully capped you can be about 95% certain that the honey moisture content is correct. Again this magical 80% number comes up - if a frame (both sides) is approx 80% capped it is a very good indication that the moisture content will be correct.
As for how much honey I leave my bees with, this year I've still got hybrid super on top of the QX above my brood box. I've got 4 fully capped traditional frames, 1 fully capped flow frame, and 2 flow frames that have 1 side half capped and about two-thirds full and the other side one-third full with nectar but uncapped. I was hoping to not check my hive again until late August but I might take one more look inside during June and make a decision on whether or not I keep the hybrid super on the brood box or remove it.