Managing Quail that Are Not in Cages

4'x8' isn't terribly large, I'm not sure it'll be enough to prevent fighting if you keep several males in an enclosure of that size. They might not kill each other, but the fighting and being mated by several roos might stress the hens and cause reduced egg laying.
I don't actually keep coturnix myself, so my answers are what I've learned from this forum..
Once done with the brooder, they'll need a larger pen to grow out, so yes, I'd have a separate one. And unless you plan on getting rid of the males at 5-6 weeks, maybe even two so you can separate the sexes - otherwise the males are very likely to seriously hurt each other.
Any new bird in the aviary is likely to get picked on, and introducing new birds is likely to cause a reduced egg production for several weeks; in general, people do not recommend mixing birds that have not been raised together. So I wouldn't put them in the main aviary at all. Just build a couple of grow out pens that have at least 1 square foot per bird you intend to put in there, separate the sexes and slaughter when they've reached your desired age/size.

 

Hi Mike. General minimum recommendation is a foot squared per bird. So I'd say 14 hens and 2roos should be fine. You can mix birds ounce they are at least 5 weeks and no more than 1 to 5 females and watching them closely after mixing. For any aggressive birds. You need to seperate the young until they are 5 weeks and seperate males to at least 6 weeks (recommend 9weeks) before cull for food. Hope this helps.