Some advice on choosing fish, as you've asked for.
First, the tank size, which you mentioned is 100 liters (about 26 gallons for those of us you understand imperial measure better
). Is it a long or high tank? Tanks often come in different shapes with the same water volume, and this can make a difference as with longer tanks you are better suited to shoaling fish that may like to swim more than quiet sedate fish, whereas the higher tank can usually accommodate the sedate fish better. So, if for instance your tank is 30 inches long, it would be good for a few groups of shoaling fish like some of the smaller tetra, rasbora, etc. You mentioned barbs, and here you have some issues, as some of them are not that docile in small spaces, plus they are generally active fish that need swimming space. Our profiles give minimum tank sizes which you will note is often the length and that is because of the importance of area for many fish.
Second are water parameters, meaning the GH (general hardness) and pH which is connected to the GH and KH (carbonate hardness or Alkalinity). Knowing your GH and pH of the source water (presumably tap water) is important as it may be soft or hard and that will tell you which types of fish to be considering. It is much easier to select fish that are fine in your water, than it is to adjust water to suit delicate fish.
Third, consider the aquascape. Live plants are useful for many fish, but not all. Water flow plays into this; fish from ponds and lakes do not appreciate strong filter flows, whereas some fish need this if they occur in flowing rivers. All this is mentioned in the profiles too.