is it more practical to start such a thing, or join it?
seems like joining one would be a lot easier, even if it's just an Australian branch
The people who create games companies aren't game designers; they're clever business people who can focus on that side of things and take pressure off the designers so they can do the cool stuff.
If you want to be a risky entrepreneur, than yes, start a big games studio and find some good talent. If you want to be a developer, join a pre-established studio.