So back on the topic of how many characters to expect in the final roster...
I think that you're looking at a minimum of 32ish no matter what. 35 or so doesn't seem that unrealistic. 40 is probably pushing it, but still not out of the realm of possibility. (Anything over that probably won't happen.)
Here is what I am basing my numbers on... What has been revealed so far + (what I believe to be) Very Likely candidates -- The MINIMUM final roster COULD PROBABLY look like this:
WARNING: SPECULATION AHEAD. Don't quote anything on this list and complain that it's not yet confirmed, I'm aware!
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Veteran Starters: (13 total, 2 unconfirmed)
Mario, Link, Kirby, Pikachu, Fox, Samus, Zelda, Bowser, Donkey Kong, Yoshi, Peach, Captain Falcon*, Ice Climbers*
Newcomer Starters: (7 total, 2 unconfirmed)
Pit, Wario, (Zero Suit Samus), Ike, Pokémon Traininer, Lucas*, Meta-Knight, Tom Nook*
20 STARTERS TOTAL. Seems like a nice realistic number, eh?
Veteran Unlockables: (5 total, 4 unconfirmed)
Jigglypuff*, Luigi*, Falco*, Ganondorf, Marth*
Newcomer Unlockables: (7 total, 6 unconfirmed)
Snake, King Dedede*, Diddy Kong*, Krystal or Other Female Char*, Balloon Fighter or R.O.B.*, Third Party Character 2 (Megamanz?!)*, Third Party Character 3 (Sonic LOL!?)*
12 UNLOCKABLES. Seems like we could realistically see a few more than this, right?
* - Unconfirmed speculated character
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Notes:
I didn't count ZSS in my numbers since (like Sheik) she probably won't have a portrait on the character select screen.
I find Tom Nook and Lucas to be very likely, due to the appearance of the Animal Crossing and Earthbound logos on the Dojo. If you want, however, replace them with any other char from the same series (Nook with AC Boy or Lucas with Ness)... I'm more interested in speculating the NUMBER of fighters in the final roster in this post, rather than the specific characters.
What do you think? A lot of this is assumption but I'd like to believe it's educated assumption.
Edit: Again, I'm presenting this because it seems likely as the MINIMUM amount of characters we could see after taking into account what I believe to be are very-likely candidates. I'm hoping (and guessing) there will be a few more. (And if we continue to get one character per week on the dojo (and assuming the dojo wont show unlockables), this number will probably get even higher.)