you might want to make sure the first fish you put in your pond are punkinseed sunfish, as they'll eat the snails..the snails cause grubs in other fish like bluegills and pike..which are not going to hurt you if you eat them but they are ugly.
you also could probably put in bass or trout, when you choose make sure that the fish you put in won't necessarily eat each other..walleye would also be good as they will clean up a lot of the messy stuff in your pond...they are also good eating.
the problem isn't really how cold the pond gets as it is how hot the pond gets, but if you have 10' deep areas then there is a cold are for the fish to go to get away from the heat..heat will kill more fish than the cold if your pond doesn't freeze clean to the bottom..and yes a bubbler to keep the pond open is a great idea but you can also build a floating
greenhouse type of thing to float out there to bring
solar heat into the pond..basically anything that is solid and clear can be built into some sort of floaty thing, and left anchored out in the pond..basically a
solar raft.
the larger the better for your solar raft, and more than one in several areas are also a great idea..best if they aren't breakable and are UV resistant as well..greenhouse wall type fabric is good, esp the double wall polycarbonite..
something as simple as 2 basement window well covers back to back with some silicone glue and some reinforcement fasteners put on a floating frame..that will give you a large open
greenhouse type solar collector for your pond.