Houston Freezing – New to the area

I am new to the Houston area and curious about the pipe freezing issue I hear many people talk about. We are in a new house and I want to make sure, as the colder weather approaches, I do everything I need to in order to minimize any pipe issues. I have a few questions:

1. When do people really need to worry about pipes freezing? Is it when the nighttime temps get below freezing or when daytime temps are below freezing?
2. I will shut off, bleed, and wrap sprinkler valve, small exposed PVC outside is foam wrapped already, I will cover the hose bibs, and there is only a small run of PVC in the attic that goes from the ext. garage wall to the water heater but that is already foam wrapped in the attic (Pex everywhere else). Is there any other precautions I need to take?