LLSIF Medley Festival Guide

Okay so here's a quick rundown of how the Medley Festival event goes:

Press フェスを開催する to start
You can choose difficulty, Easy / Normal / Hard / Expert
Choose whether you want to play 1-3 songs; LP consumption is listed at the bottom of the screen.

Once you proceed, you will get X number of songs chosen at random.
Note that the trick of quitting out of the app and try to draw new songs doesn't work.
After choosing a team, you can choose modifiers ("arrangements") to make the game easier:

出現率 - Improves drops from clearing songs (not sure about this)
パーフェクトサポート - Turns good/bad into perfect, 5 uses
EXP↑ - EXP gain up
タップSCORE↑ - Increase base score from notes
特技発動↑ - Increases members' special skill rate
イベントポイント↑ - Gain 10% more event points
体力回復 - Recovers 30% of stamina after each song

You use gold to pay for modifiers, and each modifier costs quite a bit of gold so don't spam unless you don't need it (i.e. the stamina recovery one)

As for efficiency in getting event points, quick comparison:
3 songs expert (LP: 60) = about 1k+ points
2 songs hard (LP: 24) = about 390 points
So expert on 3 songs is slightly more efficient IMO.

Apart from this, the rest of the game goes as usual.

tl;dr: glorified course mode