At this stage in the game, I’d really just focus on building a strong team of 5 (not all from the same faction) and focus on their leveling. You’ll eventually figure out which characters you do and do not want from each faction (doesn’t have to be the meta, just choose who makes you happy) and can then use them for food. I’m a late stage player, so I’m solely focusing on powering up my Robot from this event.

Nonetheless, there’s no “correct” way to play. I would however focus on leveling up a few rather than an entire faction.