both angels and barbs are semi aggressive, so your peaceful tank idea is a little shot at this point. firstly, i would definitely add more barbs - make a group of 6. also add more platies if you like those. a bristlenose would do nicely in keeping you algae free. i personally would add a small group of loaches, like yoyos, for the bottom strata - lots of fun. and maybe a school of a feisty tetra like serpaes.
50gal planted - yoyo loaches, BNs, odessa barbs, giant danios
33gal planted - praecox rainbows, gold ram, bolivian rams, sparkling gouramis, licorice gouramis, lots of shrimp
2 x 5gal planted - bettas