here's my two cents. you could do an incredible tanganyika ecosystem with that set up you have there... if i was you here's my plan:
- on either end of the 'tank' you could have two big rock piles. from there you could set up a plethora of different communities. you could have a big colony of some kind of tropheus; doesn't have to be the rare stuff. if you want some instant color and bang, i would get tropheus ikola kaiser (yellow bands). get a school of 20 small ones to start with and probably in a year's time that would double or triple easily.
http://www.cichlids.net/images/fish/trikola.jpg
the rocky ecosystem would also support fish like calvus, compressiceps, julidiochromis etc.
- towards the rocky edge and going for around 2-3 feet towards the middle, you could plant a bunch of giant vallisneria. i think it would be cool to have huge shoals of cyprichromis (40 or something) darting through that and at the surface.
http://win.afrofish.it/public/album/Lago Tanganyika/Cyprichromis.jpg
- at the edge of the plant and going towards the middle of the tank you can have huge huge colonies of shell dwellers (lamprologus sp.). imagine seeing 3-4 feet of tank space just littered with shells and having dozens and dozens of micro colonies of these guys flitting around
http://www.aqua-fish.net/imgs/articles/lamprologus_multifasciatus.jpeg
- and in the middle you could have a huge area for sand sifting cichlids like xenotilapias, enantiopus, cyathopharynx furcifer etc. etc. that are in shoals of 5-6 males and 20 females
http://www.tomstanganyikans.com/images/Cyathopharynx Furcifer Ruziba.jpg
http://virtualwords.newtime.hu/images/words/enantiopus.jpg
http://www.reservestockcichlids.com/images/P/X bathyblue.jpg
i think instead of stuffing that tank to the brim with a bunch of mbunas or some pbass, go create that living ecosystem that resembles nature and bring a piece of it back home.

good luck.