Here's my thoughts on the leak: It's real. It's just missing a few things.
The leak says we're getting:
Pac-Man
Mii's
Palutena
Shulk
Chrom
Chorus Men/Marshal
Pokémon X/Y character (Greninja'd)
(and then villager, Mega Man, and Wii Fit Trainer)
The person leaking it is credible for what we know, and already leaked Villager, Wii Fit Trainers, Little Mac, and Mega Man. However, he didn't get Rosalina. What that tells us is, if he's right and the leaks are true, is that there is a possibility of other characters getting in as well, such as Mewtwo and K.Rool. (don't get me started on Ridley)
Every Smash game, we've gotten two Pokémon characters added. Mewtwo and Pichu in Melee, Pokémon Trainer's Pokémon and Lucario (would add two to the Melee roster) gave us 6. Right now, assuming Jigglypuff is back, Mewtwo would bring us to 6, and would continue the pattern of 2 Pokémon characters per game. That said, I believe Mewtwo is a lock.
With the Kremlings being shown in Smash Run, it seems as if Sakurai hasn't forgotten them. This helps K.Rool out quite a bit, and he might just be in the game. I think he is, so that's another newbie.
Overall, that gives us 14 newcomers. That's less than Brawl, yet 2 more than the original Smash. That's not a bad amount. Expecting too many more than that is bad in my opinion, and I think we're looking at a solid roster in this respect.
On the subject of veterans, I DO believe Squirtle and Ivysaur are gone, which brings us to 37 characters returning from Brawl, assuming nobody else is cut. Don't expect a ridiculous amount either. The only character who even have a lick of a chance to be cut (and this is arguable) are Wolf, Ike, Snake, and Lucas.
If, in some cruel event, they're all cut, that would take us down to 33 Brawl characters. Add 14 newcomers in there, and we have a solid roster of 47 characters. From now on, I would estimate a roster of 45+. There is little chance of a roster of 40.