I think I'm about halfway through the game, I'm on chapter X or XI and my characters are around lv. 17; I'm just starting to get more weapon level 2 items and a little more than half of my main units have been promoted.
I have been using a very boring standard character setup, studiously ignoring most of my extra characters, especially the ones with the weird abilities ("I make ladders!" "I'm a merchant!") I mostly use the core characters plus Corentin and Julio, and typically not Benedict. (his buffs are fine, but the offensive buff doesn't seem as effective as say, another unit like the old archer who can just do more damage; the defense buff doesn't seem to do much; I guess the movement buff can come in handy, but most of the time I want to avoid overextending someone so I've actually not found many uses for it.)
I want to use Hossabarra because she's rad, but I have yet to figure out a way for her to be useful. Her healing seems too limited due to positioning, but she's too fragile to be a full paladin and act as a fighter. The old archer, Archibald (heh.) is good. I like the shaman, although the problem with her is activating the weather to boost her spells will undo the clear skies bonus that Frederica gets to her fire damage, and Frederica is a powerhouse. I suppose I could rely on the other casters, like whatsisname the green coat guy with the wind spell, to not worry about that synergy clash, but...why, when Frederica is right there