Toons and when they are useful?

So I have a pretty decent collection after spending a decent amount of dollars. A big question I have for others are which toons don't need to be 7* to be able to compete in top tier Pvp and if not 7* what * do you think they need to be at a minimum?

Some toons to start off with:
QGJ
leia
Ben
Poe
Rey
lando
Boba
ig-88

I've read things like boba doesn't become good till 6* and same for leia etc ... Is that true?