Perches: 2x4s work great, especially if you live in a climate that freezes in the winter. 2x4s are wide enough that they can fluff their feathers out over their feet and keep them from getting frostbit. Also, they like to perch up high. I have several levels of perches, some at 2ft, 4ft, and 6ft. They only perch at 4ft and 6ft. I have an old bunk bed ladder leading up to them, which helps because my coop is too narrow to get a good flying start. Also, it helps to stagger the perches so they don't get pooped on by anyone above them.
Nesting boxes: I have mine stacked, but they seem to like the bottom boxes better. My boxes are external for space, but I have friends who have internal boxes. They just have cubes with a bit of a lip on them to keep straw inside. Have at least 1 box per 4 hens.
Feed and water: make sure you have a place that they can keep it relatively clean, not under the perches. Also, consider installing a hook for a hanging feeder. It keeps them from wasting food, and keeps the mice population way down.
When replacing the walls, remember... ventilation!!! Build something that you can close in the winter for warmth, but leave wide open in the summer. Be sure to use hardware cloth, if you can find it, instead of chicken wire. Don't use anything with holes bigger than an inch. I've known so many people who use a wider gauge wire, or allow a space or two without the wire, and raccoons reach in and really hurt the chickens.
Remember the high level of moist poop that you're going to deal with, and have a plan for that. Will you have a wooden or dirt floor? Regular coop cleaning or deep litter method? If you have a dirt floor, be sure that predators can't dig underneath, and that often involves sinking some wire at least 6 inches into the ground.
What about light? Good windows can provide about all the light you need, but if you don't have enough light, they'll slow down or stop laying in the winter. You can use electric lights. I haven't done this, because I'm afraid of fires. I never use heat lamps, either, though I have friends who do.
Latches: never use hook/eye latches. Too easy to open. Use something that's a bit harder for a predator to open. And raccoons are smart!
Good luck, and
