I am a central NH "ponderite" and have just collected my first hatchling EP turtle.
My pond is about 7x12x36, with a small brook and quite waterfall. The substrate is 6 inches of 3/4" round stone over a 4" pvc filter system. I would prefer to overwinter "Peewee Lewis" in the pond (I guess for the reason of simplicity AND to keep him most comfortable with his settings, so he is happy and wants to stay). So

I've never had a turtle in my pond during the winter. I've always wanted to add baby painteds but have never had the chance. There are no native aquatic turtles in my area, and no one has offered me one (buying hatchlings is illegal). From what I've read, if the pond is ok to overwinter your fish and frogs, then it's probably ok for the turtles. You have to have it deep enough to leave a large layer of liquid water under the ice. A hole in the ice must be kept for gas exchange. The insertion of an air stone down that hole helps a lot as well.