This might sound like a lot of Stars but in reality it is not. Each song has a maximum total of 42 stars available (6 for 100%ing a song without over strums, and 36 available for challenges) so a minimum of 48 songs is required to get this achievement. But that requires you to complete all challenges on those songs, an easier way is to mix and match challenges with the power play mode (which can net you around 15 stars a song). All you have to do to get a high amount of stars from power play is select your two powers to be ones that give you 5 stars e.g. resurrection. This will give you 10 stars just from the powers, so all you have to do is play the song well to get at least 5 more stars on top of that.
To check how many Quickplay+ stars you have go to "My Stuff" from the main menu and then select "Rewards Tracker" your total stars will be shown at the bottom.