I had a Frontosa quite a while ago, he was one of my favorite fish ever. Sounds like you will have quite a cool setup.
A major benefit of a central sump is you will have one filter to clean and maintain instead of a dozen canisters. That has got to make things easier. I think an efficient easy to clean sump design will make a huge difference in your success! I would try to design a large sump in which I could change a majority of the entire systems water at the one central sump instead of a half dozen different tanks. Likewise a single mechanical media will be a lot quicker to maintain than a half dozen, one for each tank. I like your idea of sponge filters as a backup.
I think your fish room layout is going to dictate a lot of the design choices on your central sump. Off the bat you can choose a single large return pump with a manifold and balancing valves to distribute return water... or you could opt for a return pump for every tank. If it were me I would seriously consider a single big return pump pushing water through a fair sized pool DE filter then probably the manifold with balancing valves... but this is just because I have a "thing" for DE filters. One return pump per tank would probably be easier to engineer, maintain and considerably less troublesome in the long run.