This is the clan to which Kasumi, Sasuke, Mondo, and possibly Fuma belong
Fuma didn't originate there. He was invited to join them after the events of Suikoden, but it's unlikely that he did given that he wasn't with them in Suikoden 2. However, he may have just been hiding and perfecting his skill hehe (which is QUITE shabby in Suikoden as he's pretty bloody easy to spot!).
Yeah, Kage does have a merc group. Probably funded by the 20k you have to pay him to join up in the original Suikoden. Mind you, Watari requires 100k...quite a bit more.
I found Watari to be a poor man's Kage. Kage was totally apathetic and was just a mercenary for hire. However, Watari had more story to him, and seemed to have a few more feelings, which p'ed me off slightly as he was technically just hired muscle.