Pipe rather small for full grown birds.
Looks to be 1/2" to 1" diameter?
Should be at least 1.5" diameter.
Even tho they are outside all day, ventilation is important when they are inside at night breathing and pooping.
No, it is not enough.
Mama should be able to keep the chicks warm.
What is that pvc pipe structure?
Coop seems a bit small for 13 birds(11 chicks and hen and cockbird)...or are there more birds in your flock?
Maybe you plan on getting rid of the male chicks?
Where in this world are you...