I have been playing at being a banjo player for 35 years or so now. Best thing I can tell you is start right here on chordie and look up some of YOUR favorite songs, change the instrument to 5 string banjo and get the chord diagrahms. The best way I have ever found to learn a song is to really love the tune and WANT to learn to play it.
As for easy songs, well any teaching book has those-ie Janet Davis, and others all have easy versions of bluegrass tunes. But if you want to take banjo into other genres-like folk, rock, classical etc, then start looking up the tunes and have some fun.