I can answer a couple of the questions off the top of my head - the water heater's in the garage, but tucked up in the closest corner to the house - it's also blanketed tightly (earthquake straps around the blankets!). We're in California, and we don't usually get much lower than 30 Fahrenheit, and that's late at night.
It's gas-fired, and that seems to be working fine, I can peer into the base and see the blue flame when it's heating.
All the fixtures in the house are about 15 years old, the age of the house itself.
We have just now nudged the temperature dial up a little, and so far it's working fine, knock wood.