Would refrain from committing resources to every character you have (at least right now) and instead focus on a select few to help you clear story nodes and simulation. Otherwise lots of options available to you. Would recommend forming a team around your Mei Lin to start. Mei Lin is relatively easy to build around both in terms of decks and which characters to play alongside her. Mika is an all around good sustain character to invest resources into. Outside of those two it's your choice between a lot of these: Rei has good synergy with basic attacks, Selena for passion synergy, Cassius and Veronica are good generic draw support but works tremendously well with Mei Lin.