For an african, instead of the buttikoferi, I would suggest 1 kribensis ( Pelvichromis kribensis). An alternative to the krib, but is somewhat more aggressive would be 1 jewel cichlid (Hemichromis guttatus, often incorrectly called Hemichromis bimaculatus). IME, single specimens of either, have gotten a long very well with Archocentrus species, even in small tanks.
For a SA cichlid, instead of the GT, I would suggest 1 flag cichlid ( Laetacara curviceps). Alternatives to this could be a festivum (Mesonauta species) or even possibly a ram cichlid (Mikrogephagus ramirizi).
Instead of the jag, you could house another CA cichlid. This is, however, IMO somewhat riskier then the other suggestions as CA aggression is often greater towards other CA. I would consider a rainbow cichlid (Herotilapia multispinosa). A firemouth (FM), Thorichthys meeki, is another possibility, though some individuals can be very aggressive, and because of this, it is quite possible that you will encounter aggression problems between an FM and your septemfasciatus in a 29 gal., at least eventually. An FM, IMO, could work but is riskier.
For a non-cichlid, I would suggest a blue gourami( or gold gourami) or a paradise fish. Other gouramis might also be an option, but are IME and IMO not as hardy and sometimes too easily pushed around by cichlids. For a bottom feeder, chinese algae eater ( CAE) and/or BN pleco. A few zebra danios or giant danios may also do O.K. in this tank.
Of course there are never any guarantees with cichlids; every individual fish is different, every situation a fish is put into is different and fish change with age. None of these fishes will out grow your 29 gal. and IMO mixes of these types of fish work well in this size of tank.
