I think it's good that you're thinking this through. Here's my take on space; I think that you have to plan for the most restrictive scenario. For example, we like to travel a lot which often means no one is here to let them out and put them up at night (and we usually don't have our house-sitter let them out). So, we try to have enough space that even when confined for several weeks on end, they're O.K. Right now it's about as crowded as ever with nine adult birds (very soon to be eight) in 200 square feet of combined run and coop space (~25 sq ft/bird).
I think that it's so very helpful to have a completely enclosed run; one that is covered and as strong at defending attacks as your coop. That way you don't have to worry about locking them up at night in the coop and letting them out to the run in the morning.
Also, your free-ranging schedule is very likely to change over the time you have chickens either due to a change in jobs or the inevitable predator attack. I used to free-range like you but once the coyotes found our property we had to stop. I only let them out when I'm outside and even that is no guarantee, in the last attack the coyote jumped the wall and grabbed a hen right in front of me. We got lucky in that we had three and a half good years of free-ranging before the coyotes found us and I was here to stop both attacks which surely limited the number of fatalities. We got much luckier than most folks I know here in Tucson. I think our 6' block wall helped because over the years we saw the coyotes take the less secluded and protected chickens in the neighborhood before they got around to discovering ours. I can tell you, that after reading this entire thread and talking with lots of other chicken raisers here in southern AZ, it is only a matter of time before a dog, coyote or bobcat finds your flock. Not that I'm advocating against free-ranging, because I do free-range, but once something like this happens, it has an impact on how you manage your flock. I think it's worthwhile considering the impact when you're in the planning stages.
