I have an AquaStart 320 (21l) with Mosquito rasboras in a blackwater setup - should go and take some pictures of it actually, but it will have to be an night as there are too many reflections during the day.
Setup as follows:
Sponge filter with cut down airflow
Peat substrate, about 20 - 30mm depending on where it is in the tank
Oak leaves and Indian almond leaves - crushed sitting on top of peat
Driftwood with narrow leaf java fern attached
Tinfoil over parts of the light to stop it reaching every corner of the tank - it is brightest over the plant
10 Boraras brigittae
Whole bunch of daphnia - the big ones won't fit in the fish's mouths but the little ones disappear after a while
The tank you have would probably be too small for Colisa laila - they are terribly territorial and if you manage to get a pair she will spend all her time hiding from a beating.
Corydoras pygmaeus are neat, especially in a large group, but are horribly expensive. They would go well with something else in the tank like Celestial Pearl Danios, but there again, these things seem to spend all their time hiding as well as looking hunched up!
There, I have probably confused you more now!