Quail are much better layers than chickens, if you take into account feed to egg ratio. A coturnix quail hen will lay 1 pound's worth of eggs for every 1 pound's worth of feed they eat. They mature much more quickly than chickens do, the coturnix can start laying as early as 5 weeks, sometimes earlier. They are also full size at 12 weeks old (for coturnix).
As for keeping chickens and quail together? I wouldn't recommend it. Quail are best kept off the ground, unless you don't plan on eating them. If you do, and they are on the ground, you would have to worm them, about every 3 months. Plus, the quail are somewhat smaller, depending on what type you get. It would just be asking for trouble, in my opinion. You can, as stated before, hatch quail eggs under a broody hen, but I would seperate the adults.