Definitely NOT ANY DRAGONETS (Mandarins, Scotter Blenny). The water or tank size is not the factor it's the Live Rock Quanitity and quality and the amount of copepods they can produce for the dragonets taht are important. You can sometimes buy manarins or scooters that eat frozen or prepared foods, but don't buy one thinking you can 'train' it to eat prepared foods, way too difficult a task and usually fails to the death of the poor fish.
Now for good Nano fish, there are many gobies that are always a good fish. Ocellaris Clowns, True Percula Clowns, Firefish, cardinal fish to start with.
There are others out there too but for starters go with Hardy, easy to keep fish and as the tank matures and if you have the space add a different species if you want to.
Most people in reef keeping have a few fish just for movement, the real attraction is the coral you maintain.
HTH,
TB