Depends how far are you. I rented a car and came from Tokyo so I did not need a day pass. Overall its not that expensive so I dont think a day pass can save you so much unless you come from far away and need long or multiple train rides.

Would recommend to stay in the little onsen town next to the river between train station and monkey park, nice places and good restaurants. Also, the chance to have the Onsen experience, 9 different ones can be used freely if you stay in B&Bs

There are regular buses going to the park. I suppose taxi would bring you to anyway you like as long as you pay the fare and taxi fares in Japan is kinda on the high side.

Please don’t. The pool is very small and you don’t want to spread any virus or caught any in the pool and the monkeys are very territorial.

The start of the trail is on a up slope. But it’s not a long, thereafter it’s a gentle climb up. You just need to pace yourself, and along the trail, some part maybe a little narrow. When you reached the end, there is a slope where is man made stair for you to climb up. It’s a good walk and a workout for a day. So there should not be any problem. If you happen to stay around that area, after the walk, if would be very nice to soak in a hot bath in your hotel or some onsen to recuperate and ease your knee. It’s a trip that you will really enjoy.

We had the Snow Monkey Pass and took the 11:33 train (with no changes) from Nagano to Yudanakan, which I think is the Express. Looking at the pdf from the website it appears the Pass works for local as well. I can't post a link here, but google nagaden-net and under Snow Monkey Pass click on Timetable. Hope this helps :).

There are small lockers, but they are at the small shop which is at the entrance, 1.6km along the walking track. Definitely not suitable for pulling luggage along. From what I remember the lockers are backpack sized & suitable for leaving stuff in while you check out the monkeys. They require a 100 yen coin (refundable). There isn't anything anywhere at the bottom of the walking track for luggage storage, from memory.

Hello, We caught the bullet train then transferred to a local line and then caught a bus. This is dependent on where you are travelling from. Your resort would be able to help you for sure. Keep in mind that there is quite a walk up a snowy track - easy walk though - just make sure you have good shoes or boots. There are a lot of monkeys to enjoy! It’s fantastic to see 😊