You have several options but each has it’s limitations. Some options I would consider would be:
1. 2-3 Male dwarves and an appropriate number of females (some do better in pairs where others do better with 2 or 3 F per 1 M). If your local store won’t assist you in obtaining them look into the option of buying them via the internet. I’ve read only great things about Apisto Dave (apistorgammaidiots.com) and have several Cockatoos on order from him now (Due in Thrs). I’ll post when I receive them and share details of my experience.
2. Severum species aquarium. If I were to do this I would take one of two approaches. Either way start with about 5-6 Sevs, then as they grow up, watch for differences in Males and Females and see if any pair off. At about 5 inches the aquarium will be overcrowded and some will need to be moved or sold. At this point make a final decision to keep 3 Males, 3 Females or 1 pair.
3. Then there is always the option of having a mixed aquarium. To do this I would think more cover would be necessary as different species of fish have different aggression levels at different times of life and grow at different rates. This is often very interesting to watch the ‘king of the tank’ title float from fish to fish, but often leaves one fish as the runt to be run over in an unpleasant way. I think all of the fish mentioned thus far would work, but a 55 Gal will fill up rather quickly so be careful stocking.
4. One I haven’t heard yet but immediately came to mind, since you are such a fan of Blue Acaras, why not a species tank for them? I’ve never raised them but just basing things off their Adult size and lighter aggression levels I would think you could happily have 2 pairs or 4 of the same sex. (Note: Im under the impression that Acaras usually get around 6 inches, if it is true they get 8 as Sevs said then stock 1 pr or 3 same sex like with Severums).
Again, you have many options and the ones I listed are simply the ones that sound attractive and safe to me. It is impossible for any of us to decide what fish would bring you the most joy. All we can do is mention fish we are impressed with and suggest stocking levels we feel would be safe for the fish. The decisions all up to you. That’s the joy (and the frustration) of the hobby.
-Toby