For a start, I'd be thinking about the "mini" versions of the common species, so you can have the same look and feel, but without needing so much space. You could keep all of the following at SG 1.010 (though any higher and the archer and cichlid wouldn't be very happy).
Archer - Toxotes microlepis: max size 15 cm
Mono - Monodactylus kottelati: max size 8 cm
Papuan scat - Selenotoca papuensis: max size 9 cm
Cichlid - Orange chromide: max size 6 cm
Waspfish - Neovespicular depressifrons: max size 10 cm
Sleeper goby - Dormitator lebretonis: max size 10 cm
Figure-8 puffer - Tetraodon biocellatus: max size 8 cm
Not all of these are widely available, and in the case of the archer, scat, and mono you need to be able to identify them (something retailers seem incapable of doing). Tips for the archer and mono are on my FAQ; the scat is a little more tricky. Compared with Selenotoca multifasciata, Selenotoca papuensis has fewer, thicker vertical bands and the spots on the lower half of the body are much larger. Such differences are really only obvious when comparing the two species side-by-side, but roughly speaking, on Selenotoca papuensis the spots are about the size of the eyes, while on Selenotoca multifasciata, the spots are very much smaller.
Cheers,
Neale