Welcome to BYC. Where, in general, are you? Climate matters, especially when considering chicken housing.
The Usual Guidelines
For each adult, standard-sized hen you need:
- 4 square feet in the coop,
- 10 square feet in the run,
- 1 linear foot of roost,
- 1/4 of a nest box,
- And 1 square foot of permanent, 24/7/365 ventilation, preferably located over the birds' heads when they're sitting on the roost.
For 7 birds you should have at least:
- 28 square feet in the coop,
- 70 square feet in the run,
- 7 linear feet of roost,
- 2 nest boxes,
- and 7 square feet of ventilation.
The smallest coop you should keep 7 in is 4x7 -- but since lumber comes in multiples of 4 feet, 4x8 is more practical to build. 6x6 is also a good option since you can buy 12-foot boards and cut them in half.
Your huge run is *may* compensate for tight quarters in the coop, but only up to a point and only if you live in a mild climate where they are NEVER shut into the coop in the daylight either because you have closed them up or because the weather is too severe for them to go out.
My own flock is a little tight in the coop right now, but I live in just such a mild climate so my huge run with over 30 square feet per bird has compensated so far. If you live where you get snow you will need extra room for your birds to live in when they can't get outside.
Additionally, integration takes extra space.
First, you need space to quarantine away from your existing flock.
Second, you need space to set up a see-don't-touch system so that they can get used to each other without being able to hurt each other.
Third, you need extra space so that the new birds have places to hide and so that you can set up multiple feeders and waterers until the flock has fully accepted the newcomers.
Here are some useful articles on integration:
https://www.backyardchickens.com/articles/introducing-new-chickens-using-the-“see-but-don’t-touch”-method.67839/
https://www.backyardchickens.com/articles/adding-to-your-flock.47756/
And my
integration pen inside my oversized run: