I agree that an easy, maybe the easiest song, is
No Sleep Till Brooklyn with everyone playing on hard (Vocals can go on expert it's all the same). Guitar is mainly the hardest because of the solo.
Drums, the pattern is the same mainly though out the song, so it's not too difficult to get the hang of it.
Bass, is easy as there's barely any notes but might be hard for some who normally plays on medium difficulty.
Vocals, Since the song is sung by 3 or 4 people from the band all the vocals in the game are just spoken, so you can simply place your microphone against a fan or TV speaker and let it pick up the sound to get 100%.
Good luck