A quick dip of a few hours around 30 degrees is very unlikely to cause anything to freeze up, frankly.
PEX tubing generally can withstand freezing water in the tubing itself; the problems usually occur at the elbows and connectors and other fittings, which are less malleable. Leaving a faucet open or the pump off won't do anything significant to change things in terms of freeze damage (nor will it hurt anything); however, leaving the pump off is probably not a bad idea in case a leak should develop to reduce secondary damage. Leaving the water heater on is fine, and logically would be safer than having it off since there's no way the water inside the tank can freeze when it's maintained at 140 degrees. The main supply tank freezing is not a concern at all for this sort of weather because the thermal mass of the water stored in it will prevent it from freezing overnight at these temperatures.
In short, I don't think you have much of anything to worry about so long as the lows are just dipping down around 30 and the wind is not super strong and the daytime temperatures are at least somewhat warmer. It's probably not even necessary to disconnect the hose, though that's a reasonable thing to do on principle alone. (Of course, with the hose it's only the fittings that are a concern; the elasticity of the hose proper makes freezing in that part a non-issue unless you need to get liquid water through the ice.)
