A single krib should be fine in a tank like that.
Although I have noticed that when they are by themselves tend to stake out an open cave and sit there watching the world go by. No problem, you just dont see them swimming around the tank very much, unless it's feeding time. They sorta act like a troll living under a bridge, and just pop out to chase off smaller pesky fish. :lol:
If you have 2, they will either pair up, which is good, or one will chase the other, not so good.
3 or more will form a more active and social group, they will work out their pecking order and interact with each other. But as long as they have plenty of space and hiding spots they will all be OK.
They are fine in a community tank, but they might get tempted by slow moving long finned fish like male guppies :-? A krib will be fine with your danios, tetras etc, and it might be best with just one in a small tank.
Cheers
Ian