I've seen chickens sleep in trees when it never got above zero Fahrenheit for four straight days and nights. The chickens were unharmed. In a decent coop they should not have a problem but if you wish to provide heat do so. Any time you use electricity for anything you have some risks so use reasonable precautions. If you think about what you are doing you can do it safely no matter what you use for a heating element.
I don't know how you plan to run the electricity to the coop. I ran a proper wire through buried conduit from breaker box to a breaker box, all according to code by a licensed electrician. That way I could have separate circuits for lights and different wall plug-ins. That way I can plug in a power tool without dimming the lights. If one circuit goes out I don't lose the others. Heat can take a lot of amps so make sure you size the breakers and wiring properly.
I installed wall outlets so I can plug in power tools, that has come in handy several times. The lights are on their own circuit. My coop is one end of a shed so I have an outdoor light, a light for the shed part, and a light for inside the coop. A heated waterer in winter may come in handy. I built in a brooder so I can raise chicks in the coop instead of in the house since I have power down there.
My suggestion is pretty much the same as when you are building a house. Put in more outlets than you think you will ever need and put them on enough different circuits so you don't flip a breaker. As long as the amps are OK it doesn't matter what they are used for.