Did you know that your kissing gourami can get up to 12"?? He will be too big before long, fishlore.com reccommends 50gal or larger for the kissers. I am not aware of any dwarf variety of the kisser, just misinformed pet stores.
sorry for the barbs, barbs r schooling fish, u have to keep at least 6 of them in a tank, it will reduce their fin nipping habit too. plecos can grow up to 18 inches, so u should get rid of it. danios r schooling fish too, keep 6 of them as well. kissing gouramis r also not suitable for a 20 gallon tank, they r territorial and sometimes can become very annoying, sometimes they may harass other fish.
i think tetras will be the right choice as tank mates for barbs and danios.