Well, a 5x7 coop, even with all the floor space available, isn't large enough for twelve standard hens. If you ask around, most people here on BYC will tell you that each hen needs four square feet of indoor space, not counting nest boxes or roosts. The less room a flock has, the more behavioral problems occur- everyone is cramped and grumpy. They turn on each other and can cause serious injuries. Chickens with more room are happier, healthier, and easier to manage. More room also frees up management options, like being able to use the deep litter method efficiently. Your coop could at most hold 8-9 hens- if you didn't include the nesting boxes in the rough measurements you gave me. If you free range you can get away with more birds, since they will spend most of their time outside, but free ranging has it's risks. Hawks, foxes, coyotes, neighborhood dogs.... lots of hungry predators out there.
I say, if you are going with standard size hens, keep 8-9; if you will keep bantams, you can house 15-17; or you can keep a few of both. Just be aware that Jersey Giants are not standard sized hens. They are HUGE, and make regular breeds like RIR's look like tiny bantams!
The coop is looking wonderful! I especially like the large roof overhang and the nest boxes, I put my egg access door on the side and every time I open it bedding falls out. But it is what it is, so we'll see. What breeds are you looking into?
