Hello Resa....
I don't really get on the forum much at all over the weekend so I'll give you my barb observations.....
My tank's a 55litre, 40cm cube with 9x five-band barbs (4m:5f); 6x cherry barbs (3m:3f); 2x male guppies and 1x male platy.
The five-band barbs are lovely. They're really peaceful and stay mainly in the bottom half of the tank, snuffling nose-down in the Cryps, hanging out under the Anubias and swimming in-and-out of Dave the Dinosaur. The have the odd half-hearted chase of each other. When I had 5 they stuck close and stayed in the plants, I added the other four and now they're much more visible and confident.
The cherry barbs are very different. The males are beautiful deep red and keep flaring their fins and 'dancing' at each other and the barbie girls, but they have their own place each in the tank, which tends to be at the back-middle, next to a plant or the bogwood. The three barbie girls form a little group and go around together.
However; my male platy swims with the barbie girls and chases off any male cherry barb and all the five-band barbs. He leaves the guppies alone. (Though one of the guppies follows the platy everywhere, nudging and nosing him. It's very 'odd'
)
Golden and/or checkered barbs get a little bit bigger, but are definitely for a 'cooler' tank. Cherries are OK down to 22
oC, and the five-bands didn't seem to mind either. I also think, from the little I've seen of golden and/or checkered, that they're more active than the cherries or five-bands and spend more time in the middle of the tank and might scare your Colista.
Your Colista likes a quiet life in the top half of your tank, so six five-band barbs would be a great addition in my humble opionion. Also, if you go down the route of a Betta, the five-bands would (probably) leave it alone completely and keep well out of the way.
We've got sheep and lambs in the field opposite...... they bleat all night long. It's quite cute really and far, far better than singing neighbours or crows.
EDIT: on a quick re-read I see you said singing
nightingales, not
neighbours! That makes more sense