I started with something that sized with 4, then 6 birds and we soon felt they had outgrown it. It should be technically big enough, people say 2-4 sf per bird for the coop part. If you allow them access to roam the yard etc then it should be fine. They just tend to pick at each other if they are in close quarters (or mine do anyways) and the more room I have given them the better.
If I could do my first coop over again I would have gotten a bigger one from the start.... once I saw how much space they liked to have I just kept getting bigger ones and felt like I wasted my money on the first ones. That may just be me though. Your coop looks very cute, functional, and well-made though. Enjoy your birds!