warm water is not a problem, they can handle 90 degrees without any issues, Cold water however will kill them. they need to be brought in before the temp gets below 50 degrees. I would start with one in the 4-6" size, real small ones are easily stressed, and VERY hard to spot and find if you need to get them out this winter. I would also consider adding two to your pond at this size to help keep up with the algae growth. large ones can be kind of expensive and they don't eat as much as the 6"-12" size do and not easy to ship eather. Be prepared they do get large and even a large one still needs to be brought in for the winter. Inside they do far better if you have a piece of driftwood for them to chew on and be sure and give them veggie based food during the winter. In the pond they don't need all this as they will feed on the algae and plant leaves as they start to decay.