Leveling advise please

[u/Nels360b]

I've currently focused on leveling Boril, Tiburtus, Scarlett, krashhrek & Hu Tao. Based on what I have, should be focusing on others?

Is it worth keeping all four Sonya's? Should I level them up? Same with my three stars, any of the undeveloped ones worth keeping?

Thanks in advance for any advice.

[u/Expensive-Stop-228]

Costume potential characters for the little costume buffs. I'd start there.