yeah that's fine. anything lower and you're gonna want a ceramic heat emitter (CHE). it will give heat without light. i have one but have never had to use it because i keep the thermostat in my house at 66 so the furnace will kick on if it drops below that. just depends on how you want to heat your house at night
i'm not sure. i would think that would depend on your house. mine is almost 100 years old so doesn't hold heat very well. also will depend on what your enclosure is made of. if you don't already have one, get a digital probe thermometer that will record high and low temps. it will let you know how cold the enclosure got over night and you can go from there.