You’ll get painted figures from the limited editions, but that’s all. Perhaps some sort of art book or something, but nothing new for the game. You shouldn’t worry about getting anything but the game and it’s expansions and possible tree beard if you’re a completionist.
They are true 25mm miniatures I believe.
They vary in scale! None are 25 mm as far as I can tell. Closer to 15 mm for the largest models.