I guess in your case it's better to farm the butterflies instead for the first phase and focus on the red mantis after. This event should be very long since the next maintenance (aka event phase 2) is deleday to 2019/1/7. ERaid boss event s a good way to build a solid stock of Manyus, gold and that kind of things.
Focus only on the lvl 90 and 80. Avoid the others. And use a lvl1 2* girl for boss battles. On DMM players can kill a raid boss by themself in a few seconds. You just want to do the battle as fast as possible to get as much godd bosses as you can.