Your well water is well below the frost line and will not freeze - nothing to worry about. Septic - no concerns at all. Other concerns will depends upon how well your home is insulated, as some homes see water pipes freeze in temps like well see for the next few days.

You have been using wood heat is to be aware of cold areas in your home. We have been using wood all winter, but will be turning on the heat for a few days. We don't typically heat our upstairs unless we have visitors, and it can get very cold up there and don't want bathroom pipes to freeze.

Pay attention to how cold it can get under your kitchen sink - a pretty common spot for frozen pipes as the kitchen sink usually sits on an exterior wall and under a window. Many people in older homes will open up the cabinets under their sinks to let warm air circulate. I know people in really old homes that will leave their sinks dripping, as moving water takes longer to freeze.