I reckon there'll probably be between 15 and 20 playable characters and about the same number of enemy character. There's no way this game'll have the size of a regular Musou game, but on the flip side the things they're doing with the multiple weapon types (ie Zelda can equip a rapier or she can equip The Wind Waker, both with unique fighting styles and move sets) basically means she's two characters in one by DW standards anyway. Plus, the things like the large, non-player bosses, such as King Dodongo, or equippable weapons found on the battlefield, like bombs, aren't a DW-style thing at all and are a very new concept for these developers.
I wonder... will we get mounts? Regular DW has horses, and I'm surprised we haven't seen Epona.