Oops! That means pearls won't work unfortunately. You are, in fact, almost fully stocked with just the barbs because the golds grow to 4". You could just about fit a single male honey gourami and maybe a couple of dwarf chained loaches if you do it gradualy.
I just recently lost my biggest tiger barb out of a school of ten (then - 6 tiger, 4 albino) not sure if it was aggression from the two gouramis I have (one m gold & one mblue three spot), the rtbs, or the other barbs as I saw hardly any agression amongst all of them. water levels were all normal (my aqua out of the tap - ph is 7.6 - 7.8) Sorry about rambling, just thought I would add that observation to the original question...