I mean, we know for a fact from the boxart Aang, Korra, Ren, Stimpy, what seems to be live action Dora, CatDog, and maybe Krumm on the box art. Krumm is the most awkward to see but the rest are all clearly there. That already brings the roster up to 20, or 19 if Ren and Stimpy are a team character.
I would say expecting at least 25 characters seems like a safe bet. If I had to name names, I would say Donnie, Raph, Arnold, Rocko, Ronnie Anne, another spongebob rep,and Garfield are the safe bets. I also am personally betting on Jimmy Neutron and Jenny XJ9 as well, which would make us at around 29 ish characters. Which to me seems like a healthy amount to expect.
FOP is weird and I could see it getting vetoed by nick because they are rebooting it, I don’t think Timmy is in the reboot iirc. I could see Timmy being a popular dlc candidate if the game does well, which given the hype I think it will certainly make a profit and succeed if it is good.