For the 3DS, considering that it's not not capable of holding more than 35, the roster would be around the same number of characters as the roster in Melee. For the Wii U, based on the pattern on the 10 digit number (64: 12, Melee: 25, Brawl: 35), I'd say around 40 characters. The idea of having Dawn/Lyra/Hilda depends on which starter set will be next to be playable to co-exist with the original starter set.