Heh...I guess I haven't gotten there yet.
Well, I found that Sarah was basically the same as Cooke, only with slightly higher stats, so I now use Kaim, Seth, Ming, Sarah and Mack. Ming does everything Jansen does (and more) with slightly better stats, and I like the idea of dedicating support spells to Mack.
I just got to Saman, and while it was lengthy, I didn't find it too difficult. I never had to use a single item, actually, and I never died. Basically, I just gave Relax to both Ming and Sarah, which means I could set aside time to Defend in each battle, thereby keeping their MP maxed. So if I used attack or healing spells during the battle (which I always did), when I got down to one enemy remaining, I gave Sarah and Ming a chance to get all their MP back with Relax. It worked out pretty well.
I'm Lv. 28 and at the 20.5 hour mark.