Stick with what you would stock a 10. I would stick away from apistos, unless you only had a pair. Vertical swimming space doesn't mean much to many fish with the exception of angels, discus, etc. May some cory cats on the bottom and any choice of small schooling fish for the rest (tetras, danios, raspoboras, or even guppies).
Of you could be cool and start a dwarf shrimp tank!