I guess that I always seem to come across as the naysayer, but....(sigh). Although clownfish are routinely kept in 12G nanos, I personally don't think it is right. I don't think it is conscientious and that they deserve more swimming room. JMO.
As for CBS, I've never owned them but I have followed 'owners' for many years. They can be very aggressive and they CAN corner fish. I've heard that they can nail the fish when they are sleeping. Although there is no contraindication on keeping them in a nano-sized tank per se, you should be careful on their compatibility with you have in your tank.
SH