I think it'll likely be either 4 or 5, because of the way challenge rating is calculated in 5e. It assumes that you have 4 players of the same level of the challgenge rating of the listed enemy.
But if they allow a companion of each class it'll total 12, so you'll probably be able to "store" the ones you are not using and switch your companions whenever you want.
Why make a major change to the gameplay everyone is used to instead of simply increasing the "challenge rating" to account for 6?
Because most developers design for casuals and they think having too many party members makes the game too complex for them.
Yup. It's also the real reason why the game will be TB, because RTwP in the context of a cRPG is too complicated and too challenging for most gamers. Everything that can be made easier and simpler for people will be made so, from getting rid of misses to simplified spellcasting to smaller party to handle to TB combat. It's the only way to sell more than a few hundred thousand units.
