guppies only need (well not really) live plants is if you want babies. Although same can be said about mollies! its just some where for the fry to hide while they grow up.
i would say 100% to corys,
just amke sure you get them in at least 3's. VERY entertaining fish to watch
i
have 2 bronze (boring looking, but very active)
and two unkown (very pretty, will upload a pic in a bit) corys will also clean the bottom of the tank of any left over food meaning over feeding is almost eliminated
neon tetras are an obvious choice, but so pretty. It depends on what your looking for really