40B suggestions?

I have a 40b that I'm currently using to grow out some Cryptoheros nanoluteus. Once I have a pair this tank will be available for a new project.

My first thought was a Peacock harem, but with a tank this size that pretty much limits me to a species tank. Not necessarily a bad thing, just limiting.

My other thought was a Neolamprologus leleupi pair, with 4x synodontis lucipinnis, and 6x school of either celebes rainbowfish, madagascar rainbowfish, or lake inle Danio. In my head in seems like there should be another cichlid in here, but with this footprint I'm not sure there is enough room for another territorial fish.

Any thoughts/suggestions on how well this might work, or good alternatives?

Thanks
Adam

Just for some additional information the tank is filtered by a Toms rp3 wet/dry, has two Ebo Jager submersible heaters, and lighting is DIY fixture with three hardware store clamp lamps with 13watt 6500K CFL's, and a substrate of dark aragonite sand.

I like the sand, although I've read that Leleupi shouldn't be kept on a dark substrate if you want their colors to be vibrant.

My only problem with the RP3 is the amount of microbubbles it makes. Not sure how to fix that.

Thanks for the reply. Those caudopunctatus look pretty cool. Can you suggest any other smaller compatible species. If I dropped the leleupi which can get 5" and stuck with something smaller I could use Psuedomugil Furcatus which would allow a larger school and still have a smaller bioload.