What i could i have like 3 and thats it?thank youFor the 20g, unless you're looking at guppies and neons, not much of a community is to be had.
Exodons Paradoxus are to me the smallest "true" predators one could have that doesn't require to be alone, but your tank is just a little bit small for a shoal and without a tight group, it's a miss more often than a hit.
You could try a small group, but I don't advise it.