DONT DO IT. While it may work sometimes, it is a fact that having quail around chickens can prove deadly via disease.
If you play Russian roulette, there's only a 1 in 6 chance that you get the bullet, so chances are you won't get the bullet the first time you pull the trigger. But if You pull the trigger enough times, the odds won't be with you for much longer.
If you know the repercussions of what could happen, don't risk it. It's not only unfair to the animals that you could have prevented from getting sick/dieing, but it will save you lots of time and money in replacing your whole flock in the future. Just do a quick search on here for mixing quails with chicken or mixing chukars/pheasants/turkeys or whatever with chickens, and you'll finds loads of valuable information, it gets asked quite frequently.
Definitely plan on doing a separate enclosure, and good luck to you with your venture on quail. They're definately addicting!
EDIT:
I forgot about the cold hardy part. Most all species of quail are cold hardy birds. Whats species in specific were you talking about and that will help in giving a more accurate answer. But for what most people get, both bobwhite and coturnix quail are very cold hardy birds.