Our winter minimum is 45° and I don't bring any of my plants inside for the winter. It always warms up to room temperature during the day (high 60s/70s) though. You can use that as a general guide for how much is guaranteed safe, and then start taking chances when it gets closer to freezing. I can't help you there but you probably want to avoid leaving the plant out in freezing (or near-freezing, because you never know) temperatures. And especially avoid leaving the plant in wet soil when it's that cold, because the combination of cold and wet is extra lethal. Consider cold temperatures as a signal you should be watering less often.
The sun this time of year is excellent if you have it. Much less potent than early summer, much kinder to the plants, much less of a hazard in comparison. But definitely follow Karen's advice and make the adjustment to full sun gradually, over a few weeks, coming from the shade. So as not to shock the plant and then maybe make it somehow more sensitive to the cold, given it's already going a bit sideways. Those furry spines are like a sunscreen, and if I had to guess, your plant should take the sun very well. I would think it would suffer from too much shade, like most prickly pears.
I can't speak for the flop, because my prickly pears do that too. I sort of let them self-prune (usually this happens at the end of our months-long summer drought) and it works itself out over time. Just make sure you don't overwater, and use a fast-draining mix with about half pumice or perlite (which helps guard against overwatering).
