If you have the space, the larger the better since the birds will be happier and you'll have more flexibility to grow. 4x4 is awesome for 5 birds and I would say up to 10 comfortably.
Quail are gamebirds and unless you really tame them it's going to be traumatic to try to clip their wings. As in catching them and clipping their wings could stop them from laying.
It's better to build your cages to avoid any problems related to flying. They mainly just hop and run around anyway unless they are spooked. If you are keeping them indoors and there won't be dogs or anything running up to the cage and startling them, they will rarely use their wings.
However, they WILL start flying when they're about 1.5 weeks old in the brooder. Wouldn't you?