From Koyasan to Kawayu with suitcase

Hi,
I'm traveling from Osaka to Koyasan and plan to stay there one night and continue to Kawayu Onsen. I found out that there is only one bus per day. But even worse I jus read that the bus has no place to store suitcases. I travel very light; My suitcase is small (Total measurement 117 cm; they allow 90 cm). How strict are they?. They say I can pay the same as for a child to put the suitcase there, which I would do, but they also say not for sure in busy season. If i get there and I am not allowed to travel it seems I'm stuck. Do uber, taxis or private transportation exist?. Should I better try to go to Koyasan as a day trip and then go to Kawauyu through Kii Tanabe? I would hate to miss staying at the temple at Koyasan, but I'm not finding a way out. Help!!!
Thanks for your help

Just go with a small bag for 1 night and ship your luggage to your next hotel by TaQBin. Then you are sure you can get in the bus. No nervousness.