This is far easier than it has been in other games. The order of the Endless Setlist is no longer slowly progressing through the easy songs to get to the very hard songs, you get a mix of difficulty all through the setlist. Second, you will get a break in between every song and you don’t need to worry about the Bladder of Steel. Finally, you can turn on “No Fail” if you really want, and pass every song, but it really isn’t needed since you can change difficulties on each song.
You will have access to the Endless Setlist as soon as you boot up the game, either by going to “Play a Setlist” and choosing it, or accessing it through the Epic Rock Band 3 goals in the Career Goals menu. This will take about six and half hours plus any breaks or retries, so set aside a solid day to get this done.