plant it, cycle it and care for it and you'll have no problems with 10+ kuhlis in there. They create very little bioload, so the plants and careful monitoring should keep water quality very stable. Although mainly a bottom dweller, they sometimes like to swim vertically, but love to play on vertical decorations, such as plants. Although a 10 is kind of small, you might just get away with 20 kuhlis if you're careful. However, in a tank that size, 10-12 would probably make for a good enough show.
They love to be in numbers, so they don't really need a lot of room to spread out. Since they fit just about everywhere, you don't have the common problems associated with crowding, i.e. aggression, water quality and space to move. Kuhlis are a fish you can push the numbers on more than other species, so long as you pay attention to water quality.