How to stock my fish tank?

Chilchilids are fish that get up to a foot and would sufficate in a twenty gallon unless you bought some dwarfs. Angel fish are tall fish that need to have an aquarium 18 inches or higher aquarium you could only fit one or two in there if it is tall. platies and guppies are cool if you don't mind all the baby fish that pop up every week. Tetras and barbs are cool. I'm not sure about the dwarf gourmis because males tend to fight in big tanks