Shouldn't be a problem leaving them out at night. Cold isn't so much of a worry as heat is. Lots of people on BYC putting their chicks out quite early ... but since they almost have their feathers, could wait until then I guess. How old are they?
Our chicks were 3 - 4 weeks old when we got them, which is the standard around here. Kept them in a small coop in the garage. Had a race to get the real coop done before they outgrew the one in the garage. Took them outside and kept them in a dog cage during the day ... like you are doing ... and they loved it. Got where the rooster started struggling every time we put them in at night, because he didn't want to go back to the garage. Put them in the coop the minute it was done. Had to sit them on the roost 2 nights in a row before they would go up by themselves (have a ramp to the roost but they seldom use it anymore). It went very smoothly.
Our biggest threat here is (and was) hawks, so just had to make sure the coop very secure.
Another good website you might like is the-chicken-chick.com It has a lot of info and good videos which are short, informative, and entertaining. Taught me a lot ... actually found that website before this one.
Apollo and Rocki are cute names. Our rooster is named Reggie, hens: Honey, Mattie, Hilde, and Hermoine. Hermione is AKA Tricky ... she is very clever.