i have a waterer both in the coop and 2 outside, and my feeder is inside so it doesn't get rained on, it's a matter of preference. but if it is hot then it's best to put a waterer inside as well as outside. no such thing as too many waterers!
sure. roost space is very important about 7'' per bird, if they have plenty of run space they will probably be okay, you just don't want 2 roosters in that size coop
barred rocks are full sized birds so for them it would be about 3 square feet, birds like jersey giants need more. however i have 7 chickens in a 18 square foot coop and they do fine, they have a 20x20 run, so you could probably do 4 or 5 maybe.