I must apologise. I am canadian and am just a couple days old on the form. 25leter.. If i am right thats around 5 gallon Maybe a bit more. I drink around that much coffee everyday lol. Tbo i would be more inclined to set that up as a micro saltwater tank. Inverts and coral..
Fresh water i would keep it very simple. Very lote stocking.
Just to cleare tue smoke a bit. But most of those smaller tetras are my go to's for easy care tanks. Being so resilient and being in a smaller micro managed tank. They seem to fit. What i ment in quantity is 1 of each and maybe 2 or 3 tops. Variety and color are what most of my clients want to see.
1" per gallon in freshwater is the rule of thumb. At least from my time in the hoddy.
The other smaller fish i fall back on for a different look would be the honey gaurami.
Then again i have the recoures to move fish from tank to tank. Also i use grow tanks. So maybe im just more used to moving thungs around and continually stocking tanks.