I say, to go with choosing the most popular ones to go first.
For the ones that have an equal high score, maybe get people to vote between them to get the MOST popular out of each group.
G1:
Memory Seishun no Hikari
Furusato
Renai Revolution 21
The Peace
* Get votes between these 4*
G2:
Do It! Now (4)
G3:
Pepper Keibu (6)
The highest is Pepper Keibu (6), so that should be the next single, then Do it! Now should be after it, then whatever is the highest for the G1 go after those two ????