Heres my thoughts - Pearl Gourami will get too large as they max out around 12cm in length (they are stunning fish and my favourite gourami). Harlequins look fabulous in groups. Rummynose also are great in groups, they may spawn in your tank (they are egg scatterers), mine certainly did but it is not a common occurance. Black neons are also great in groups, a bit more prone to disease than harlequins and rummynose. 2 GBR's (for the life of me I cant think what they are). Do you mean GBA's - golden blackeyed ancistrus? So harlequins, rummynose and black neons are all compatible and it depends on whether you want several smaller groups of fish or one larger one. As far as gourami go, there don't - to my recollection - seem to be any mid sized. They either group larger or are the dwarf species, and dwarf species are susceptible to stomach issues. JJwooble on here has bred dwarf honey and is selling her young ones at the moment. Possibly being NZ bred they will be healthier. If you decide not to go gourami have a look around for another feature fish.