I haven't opened our box yet (just arrived today and bedtime just arrived), but I also have the Plan Barn here for Christmas. We opened the barn box to measure and decided that about 4.5" to 5.25" tall was ideal for bigger animals, like horses, cows, etc.
I didn't get Hape farm Animalz, we went with Holztiger for the barn...but we did get a lot of zoo Animalz for stockings.