I am very fond of the Bolivian Ram, M. altispinosus, and provided one grasps a few aspects it will make a truly wonderful addition to a community tank. I don't know about "centrepiece," this depends what one means by the term. The Ram is not large, and he is a substrate-level fish. They eat from the substrate (the reason for the genus name, "small eartheater") and they love plants for cover. A solitary male, or a bonded pair; a group maybe, as you have the space. I've never had more than the solitary male long-term so I don't know just how forceful the males might be in managing their territory in such a situation.
I acquired a male from one of the best local shops in 2008. I housed this fish in my 5-foot 115g Amazon Riverscape [the photo in post 34 is this tank then, but I can't see him so the photo below shows him], which also housed 60+ wild-caught Corydoras (some 12 or 13 species represented), three or four small loricariids, and over a hundred upper characins including marble hatchetfish, pencilfish, and several tetra species groups. The Ram would poke cories away from "his" tab/disk/pellet during feeding, but nothing serious ever developed. He was in his tenth year when he just died, which I considered pretty good for a fish with a 4-5 year life expectancy.
A pair must have accepted each other and bond to be successful; this has to occur within a group of the species, often in the store tank. Even then, divorce is still possible. I gave my Ram a female in 2009, and with the benefit of hindsight and what I now know, they never "bonded" and it was doomed from the first. They spawned four times, then he had enough and killed her. I left him on his own, and for another eight years he governed this huge tank.
I was sitting in front of the tank one day and noticed the nine Bleeding Heart Tetras were in a tight shoal mid-tank, not moving. I sat there wondering why, and then I saw why: one of the tetras swam away from the shoal and out of nowhere the Ram came up below them, and they quickly re-formed a tight group. This went on all day. Obviously the tetras has annoyed the Ram and he took matters into his own "fins" and laid down the law. BH's are not what you would call wimpy fish (for a tetra anyway), but they had no intention of disobeying the Ram. Fish communicate with pheromones, in this case cross-species with allomones, and the Ram evidently made his case loud and clear.
You have a multitude of options for characin tankmates; only real criteria is that they be peaceful species, with no propensity to possibly fin nip.
