This event doesn't offer much and is half finished anyway; spending all your seeds trying to finish it is a bad move with Icarus so close. Use natural regen BP and the BP given from rank up to get some of the rewards, but your immediate goal should be getting Vine and working on your weapons since Ixion is coming and that is not an easy fight at all.

Cybele and Oberon are irreplaceable until you get your souls together; I agree with getting Zephyrus (in the gem gacha if you don't have her).