Hey! I’m actually super new too, so I’m not sure how much help I will be, but I can try!
For starters, it seems like most characters are, at the very least, serviceable in the earlier stages. 3*'s have a lower ceiling but it’s a lot easier to raise them. So, until you have someone to switch them out for, I’d raise whomever fits your team best.
As for what type of team or comp you should make, base it on how you like to play. One of the things I REALLY like about this game is that you can kind of set things up to play how you want. You love your buffs? Play a couple supports, a debuffer or buff remover/tank, and throw Luna out there and watch her absolutely decimate fools. You prefer to go balls to the wall damage, play something like Luna, Mercedes, maybe Ken and someone else and dumpster. And until you feel comfortable with your heroes and their interactions with each other, I’d just throw them together in random comps together and see what happens.
Finally, from what I’ve been able to figure out, the equipment and artifacts are just as important as anything, so MAKE SURE you are updating those things as you go.
Man, really seems there should be a better or more active community for this game. Right?