3 opaline gouramis (1 male, 2 female)
8 golden barbs
8 black skirt tetras
6 cories
1 RTBS
Looks a bit heavy of a heavy bioload for a 40 gallons. Let's do a very basic inch/gallon calculation (and folks, i am aware of the limitations, but it's an easy way of illustrating something you might feel instinctively):
3 opaline gouramis 3x4 inches= 12
8 golden barbs 8x 2.75= 22
8 black skirt tetras 8x2= 16
6 cories 6x2 (though bronzes and peppereds can grow to 3)= 12
1 RTBS= 6
-------------------------------------------------------------------------------
68 inches
seems quite a lot actually and the barbs are not small waste producers. I have a feeling something is going to have to give. Also, quite simply visualising this tank, I have a feeling that there is too much going on in it.
At the bottom, I would choose either cories or RTBS. I'd also be worried about the cories being intimidated. They don't understand about territories and RTBS most definitely do. Maybe you'd be better off with a small loricariid, something like a bristlenose.
I think the golden barbs would probably be ok. Eight is almost certainly better than 6. But it would be hard to cram in both those and the tetras and the gourami. My feeling would be to just have the one school of barbs - they are very active and will fill that tank with activity. Or you could have a school of tetras.
Or a school of danios- have you checked out the pearls? They don't look that brilliant in the lfs, but once they are established in a home tank they develop a lovely irridescent sheen. And zebras are always good.
I think an opaline or golden gourami should be tough enough to hold its own against the barbs or tetras, but this would be a good question to put in the anabantoids forum.
I would not have more than one trio- males tend to be very territorial with each other and the opaline/golden ones are some of the worst. You could always keep just one gourami; they are not schooling fish and would not feel lonely.