FWIW, I'm a newer quail owner, after having flocks of chickens and ducks for several years.
My 6 jumbo coturnix females, ready to lay any time now, are in a 12 sq ft (26 inch by 6 ft) outdoor cage/pen. No wire floor, just peat moss, dirt, and pine pellets. I give it a once over daily. They're on a patio, with potential for neighbors nearby. They seem quite happy, but the hot wet smelly season hasn't started yet. I personally would worry about any less than 2 sq ft/bird.
Maybe someone experienced like
@Nabiki could comment on the following thought of mine: Also not sure how much they'll actually be on the wire in your case, since they'll have a natural footing area to get off the wire. So if they were to spend most of their time off the wire, the actual square footage they use will drop, and the poop smell might increase in proportion.