Unless pet shops in Oz are a LOT different than those in the USA, I wouldn't get chicks there. Go to a breeder or hatchery where they are masters of chicken, not jack of all trades pet pushers.
With regard to "introduction", having them in pens with a common wire wall or as you said, cages close together, lets them size each other up and start to sort out the pecking order before they can peck. But as another person posted, it might be easier with younger birds than adults. Keep in mind that the ones you have now will be 9 weeks old when the day olds are fully feathered and ready to go outside at ~4 weeks.
Um, you just agreed but flipped the temp where the girls are more likely to survive than the boys. So which is it? "Girls can handle it NOT being as warm as the norm" or "Girls can handle it being warmer than the norm"?? OR is it BOTH and the "easy description" is "Boys don't fare as well as girls if the temp is outside the normal incubation range?
Bruce