I'm guessing 45 max., meaning 7 new, unrevealed characters.Considering there are a lot of candidates for being dropped we may have to say goodbye and hello to a few. I know that Sakurai is trying to keep cuts to a minimum though so if an oldie doesn't get in they ran out of time, rather than them being replaced.
Lol, wut? That would be awful...
Smash 64 - 12 characters, all are technically new, so 12 newcomers.
Melee - 26 total, so 14 newcomers, granted we had a few clones. This is counting Sheik as separate, of course.
Brawl - The game says 35, but if you have Sheik separate, count Zero Suit separate, and count Pokemon Trainer as three characters instead of one, you'll have 39, so 13 newcomers essentially, plus the newcomers who are replacement characters like Ike, Toon Link, etc.
So ASSUMING that there are no cuts, we SHOULD be getting roughly 12 newcomers NOT counting people who'll replace veterans like potentially Zoroark. Any less just feels wrong, and I personally don't like the idea of Sakurai teasing us for 1 year and a half, 6 or so years total to basically give us 7 new characters, when there are SO many amazing and borderline neccesarry characters to be added, and lets face it, this will probably be the last Smash Bros. game, at least developed by Sakurai anyway.