You would be able to put in no more than 2 fully grown Bandensis. As juveniles, you may be able to keep 5-6.
The larger the tank the better. You will have less work and more success the more water volume you have. The nano craze does not change what has been proven for a long time. All it proves it that a smaller tank can be done. However, if you would like to have a nano aquarium with demanding and delicate animals, extreme care and monitoring need to be done to ensure you are giving whatever it is that you are keeping a healthy environment that they can thrive in.