If you drain the water, be sure to turn the hot water heater off first. Make sure it's full and you have water coming from the hot water taps before you turn it back on.

Given the forecast, I'd go closer to 60 on the thermostat to give you a little more time before things freeze up. Also, leave the doors open to any cupboards on outside walls that have plumbing in them (typically kitchen or bathroom sinks).

If you do have a freeze, you'll want to be very careful about turning the water back on. Wait until the house has been warm for a while, then turn the water on just a little until the pipes refill, then gradually open it the rest of the way. This way if you have a leak, you have a chance to identify it before you have a geyser. Homes aren't always plumbed with drainage for freezing weather in mind and there may be pockets of water that don't drain.