I have 21 Congo Tetra in my tank and they look stunning and shoal amazingly well. Mine are vigorous feeders for flake, granules and all sinking type wafers and frozen foods. I have never seen them eat or munch any of the plants.
Keep a mix of females and males, I keep a 2-1 ratio of females to males to even out the attention of the eager males when they want to breed. The females don't have the most interesting colour but by having them around the males have much stronger colour and will show off to each other to be the alpha male.
When mine want to hide a bit they sit behind my large bog wood but this isn't very often. Most of the time they sit in the middle of the water column.
Select stock carefully as colouration is variable and they won't colour up fully until quite mature.
Andy