The character select screen seems to indicate 4 pages with ~12 characters each, in which case
we've seen all the characters already. I guess it's possible that they're hiding something, but for now, I'm rolling with Occam's razor. This is probably it until at best post-launch.
Personally, I'm a little mixed on World's seeming focus on mooks. On one hand, picks like Pokey and Cataquack are very funny, but on the other, it feels like they didn't even get the essentials before diving headfirst into the bargain bin. Mario's cast of spinoff regulars isn't even that big, and getting folks like Peepa and Rocky Wrench (separate from Monty Mole!) over actual named characters seems kind of a waste.
That said, day 1 Cheep Cheep main if it has a green costume. Gotta rep my boy Mr. Kipper when I can.