The thing is, different people think of different things when you say 'How many characters are in the game'.
Are we talking about playable choices, drivers, vehicle forms, which platform are we talking about, what?
Me, I go with actual playable choices on the character select. Over all the different platforms, this totals up to 29 actual playable choices. But that doesn't mean that there are 29 playable choices in all platforms (in fact no single platform has all 29). Some drop down to the low 20's, some instead have high 20's.
Why is this? Well some platforms have characters that are unique to that platform. I'm not going to say which, that's part of the fun of the reveals! Some are SEGA characters, some are not. Don't bother asking
Playable choices doesn't necessarily equal drivers either. Not as we're talking passengers or hood ornaments, counting those would indeed be cheap, but you know this is game all about transformation, we are doing things with the vehicles that we've not shown you, that are going to really surprise you.
So yes I get that it's fun to debate who is right and who is wrong, but at the end of the day, you can measure what's there in loads of different ways. Across all the playable vehicles, there are currently more than 90 different forms (as each vehicle has a land, air and sea mode + you've not seen anything on the All-Stars...) and who said each vehicle was limited to a single driver... Or indeed vehicle type per surface.
Wait and see. This is why whenever you ask us anywhere, we can't give you a straight answer. Well that and the NDA's.