It really is weather dependent, and to an extent, temperament of your birds dependent. If you're in an area that gets cold winters and snow, it's pretty risky giving them such a small amount of indoor space, as they tend to spend a LOT more time cooped up over the winter months, and that's when picking and bullying due to overcrowding typically occurs. But if you're in an area that has pretty mild winters, where they truly are outside all day, all year-round, your space would most likely be fine, as long as you have a nice sized run or free range.
Also, it'll look pretty roomy, even with nine, until they're about 6-7 months old, and that's when you'll see the crowding...