No mention of aggression was mentioned. My view is that the groups of the characins will each contribute more to this aquarium. I think you will find this long-term.
I would not risk any betta in with these shoaling fish. As for the Apistogramma, you would be highly unlikely to have successful spawnings with Corydoras present, but aside from this, they are OK together. My Bolivian Ram used to get annoyed with some of the cories when feeding from the substrate, but he would push one aside, and nothing beyond that, and they being true to their nature did not take umbrage.
Bolivian Rams. A group...this is risking it. Males are territorial. Some more than others, but if a pair should form the male will most likely take control of the entire tank. Other Bolivians may or may not be killed, it depends upon the individual fish. This species was first imported by Horst Linke and Wolfgang Staeck in 1985, and their reported habitat observations suggest that this species appears to live in solitude (individual fish alone) apart from reproduction periods (Linke & Staeck, 1994). Understanding this should tell us something, that "groups" are risky at best. In nature, the other rams can and will readily leave the area if a pair makes their intentions known. This cannot occur in the aquarium, where the individual degree of each fish's inherent behaviours really matters if it will be success or failure. A dominant male will make it clear this tank is his, and the other rams will read these pheromones, even if physical aggression is non-existant. The stress this causes makes things still worse. My male Bolivian in his 5-foot 115g tank spawned four times with a female I added, then overnight he killed her, probably because he had had enough. All the fish in this tank knew he was the owner, but he never physically attacked anyone except a cory annoying his meal time, but that never came to anything more serious.
"Schooling" technically covers marine fish that remain in tight formation to swim, avoid predators, and catch prey. The latter especially, the "hunt" together in a sense. This may apply to a freshwater fish species, but not one I know of (my knowledge of species is most assuredly quite limited) and not rummynose. But, they are probably the only characin (that I can think of) that remains in this fairly tight formation all the time--except when they feed, at which time they are individual. They also continually swim lengths in any aquarium I have ever seen them, including my 5-foot tank years ago. And videos of them in nature show them actively swimming like this. In all thee years I had this species, I never saw them when they were not swimming actively, though they do stop at night obviously.
