Well since they played the Fnaf 1 song in the credits of the first Fnaf movie, I don't see why they wouldn't play It's Been So Long in the credits of this one

I honestly think the redesigns look cool

Plus the redesigns happened since some of the characters were Nintendo IP characters like Bob, Boopkins, and the SMG4 and SMG3 Mario designs. It's a copyright issue, mostly explained by the 2022 Wotfi arc

Mr Puzzles for example

More characters being introduced means more possibilities for comfort/favorite characters