I guess it is possible. Its a old method that my brothers always used and i have used to raise all chickens i have ever raised with no issues. Am hoping to get a heat mat at some stage though.
Average day probably 17 Celsius, night 9.... really hard to say. One day will be 20, that night it could drop to 1, next day 3. Next day 25. So kinda hard to say.
May just have to run a extension lead out to a bigger cage in the yard for a while.
Oh and yes they are very cute
MT