Party Size

[Shauna]

and in S5 you need 18 battle-worthy characters for the final dungeon

I remember having to do that. Barely scraped myself through the final couple of boss battles. xD Good times though.

I dunno about optimum party size. Depends on the size of the cast, as Bunny said. But, if I've been playing Suikoden, going back to a small party is just no fun. :{