We have 2 boxes for 6 hens...even though they all use the same one. Most seem to prefer to share so if you have one for about every 3 or 4 birds, I'm sure they'll be just fine.
We have two perches...well, they get into the rafters as well, so I reckon it's really 3, LOL. We offer a 2 x 4 on it's side so they can flat foot it if they want, and a tree branch that's about 2 inches diameter, so they can clutch if they prefer. Our coop is really too small for them to fly, so we built a little ladder they can climb to get up there YN is right..don't have anything at all under the perch or it'll get pooped on...including food, water, nesting boxes or other birds LOL.
We keep the food and water outside...we prefer that they only go in the coop to sleep and to lay. Come winter, we'll probably have to have some inside as well so they don't HAVE to come out in the really cold weather, but we don't get a lot of that, so it will just occur on a day to day basis. We close the coop after they've all gone to bed and open it at first light, so they have access to everything all day long.