Jeanna, i wouldn't reccomend putting day olds in with older chicks. my chicks are four weeks old and when they were 5 days i added to black sex link 2 day olds and even at that young age they kind of picked on them for two or three days. until they got to be the same size. i wouldn't put anything younger in with them now as i know they would pick on them. they are all trying to decide pecking order as it is

. i bought one rooster and 8 hens, he has just this week started asserting his roosterness to the hens. what you might want to do is raise the day olds separate but next to the older ones so they see them. when they get to be the size of your five week olds then trying putting them together, at least they will be able to peck back or get out of the way of the older ones. 40 to 50 at night is still a little chilly. when you say outside do you mean in some kind of building but out of the brooder? i would say if they are in a building and you hang a light at night when it gets cool in case they need the heat they should be fine. they will be ok during the day. good luck