Just because a character has been overly showcased or presented in demos etc doesn't mean they will start. In fact I think it will mean people will play the game heaps when they first get the game just to unlock those characters. In saying that this is what I believe will be the starting and unlockable characters:
Starters from confirmed characters list:
Mario, Peach, Bowser, Rosalina*, Yoshi, Donkey Kong, Diddy Kong, Link, Zelda, Samus, Kirby, King Dedede, Fox, Pikachu, Charizard, Olimar, Marth, Pit, Villager*, Wii Fit Trainer*, Little Mac*, Mii fighters*, Mega Man*
Starters from likely characters:
Ice Climbers, Wario
Unlockables from announced Characters:
Palutena*, Ike, Lucario, Greninja*, Luigi, Sonic, Pac-Man*, Zero Suit Samus, Shiek, Toon Link
Unlockables from likely characters:
Captain Falcon, Ganondorf, Ness, Jigglypuff, Chrom*, Chorus Men*, Meta Knight, Shulk*, Game and Watch, R.O.B, Wolf
If Mewtwo, Ridley, Isaac, Roy, King K.Rool or whoever else makes the list, they will be unlockable. I get the feeling that any newcomers or preciously cut characters announced (eg mewtwo + Roy) announced before the april direct will be given either an unlockable tag or included as DLC if the game will go down that route.
If Lucas returns, he will be a starter, although sadly I see him getting the cut.
Mii fighters and Mega Man may well be unlockable characters, whereas Zamus and Shiek could be starter characters.