One big problem of the ouya is the "missing" touchscreen.
Because you just have the touchscreen on the controller will make it different to navigate through normal apps.
And most normal apps wont have a controller support.
Maybe a mouse will fix the problem.
They will have their own ouya store where you can find games. This store has just one set of authorizations(i.e. read and write rights, internet connection, etc.) for all games.
If they will implement the normal store is not clear. I guess they will not. But you can upload any apk manually and you probably can install the play store by your self.