Oh, I don't mean that they LOOK crowded together..it's that if you do some research you'll find that you need a minimum of about 3 sq ft per bird. Recommendations vary from 2 to 4 sq ft depending on the breed size, temperament etc..but 3 sq ft is pretty much an accepted standard. Your coop is 4'x6', so that's 24 sq ft, which is an acceptable size for no more than 6 to 8 birds. If you go up to the four sq ft per bird standard, that's room enough for 4 to 6.
The run is a different story altogether..I've seen a lot of figures thrown around, but 10 sq ft per bird is a pretty common number you'll hear. So let's assume you have 5 chickens..that's 50 sq ft of run space, or depending on how it's configured roughly 6'x8'.
Ventilation is another issue..this article is very informative and goes I to depth regarding size and types of ventilation as well as the reasons why it's so important..its not just for the summer heat!
https://www.backyardchickens.com/ar...-there-and-cut-more-holes-in-your-coop.47774/