Personally, I see Demon Path as more of 'the second half of the game' rather than just optional content. But I'm probably alone on this.
Anyway, taking all of Tal's advice to heart. With the fortuitous arrival of my copy of Soul Nomad from America (I Love You, Mom!), I had a few moments to look over the specifics of my endgame group.
As it turns out, Danette, Layna, and Revya are incapable of having their Field Tactics charges increased by adding -any- generic units, so they count as unique classes.
Also, I don't have a save with the temps Levin, King Medeus(sp?) and Walnut. And I'm not sure which bosses would be worth stat-topiccing.
I also scoured the Decor(Equipment) list, and the only Decor worth mentioning is the universal stat-blocker, which is storebought, cheap, and consumable (though it stays equipped for a full battle). However, since one of these can technically work on up to 9 characters at a time, and they cost a measely 500G (endgame is about 5000000G?), it seems fair to consider this legal.
I'll do some tests on characters' Match Lists, but the in-game Help files break it down as Melee>Ranged>Magic>Melee. Tricia > mages hype begins.
Vitali and Pinot are classed as 'Special' (healers), and don't fit into the Match triangle. But I think they have innate Match advantages against certain classes, which I'll have to test.
I'm assuming that all characters counter, a la Fire Emblem.
-Djinn