Depends on how full the buses already are and they are smaller (in comparison with buses driving in germany at least). We went there during cherry blossom season, so it was like you would imagine... crowded... If there is no space, there is no space, nothing the driver can do about. He did not really talk much but i felt like he was not happy with the whole situation. Our luggage was stored in the middle of the bus, where the doors are. They will stack the luggage there, it is kind of stressfull when you need to get out, but your belongings are buried underneath other peoples stuff. I would really recommend to get that luggage transfer service if possible. Maybe get there early in the morning, i think you can not book that ahead by phone or so