Thank you for questions. You can fully enjoy this town in a day:) We are very sorry Kusatsu Sirane mountain and Moto-shirane mountain is not open in thi.s season.(open at April or so) And ”Yugama" also. we hope you will have a good trip.

I know it is too late to respond to you query. Anyway, If you are interested in visiting hot springs, I strongly recommend you to select certain part of Japan, such as Gumma, Nagano, and try to visit various spas in the area, rather than moving around all over the main island. On paper, you might be able to design an itinerary like yours. However, yours is a little too hectic to visit from hot spring to another to make you feel tired, rather than relaxed. Most of the spas you mentioned are in the mountainous areas, connected only by bus, rather than by commuters trains as found in Tokyo.

it's about 4 or 5 ours. You can take bus from Shinjuku or Shibuya, or train from Tokyo or Ueno. Yes, you shoud back to Tokyo. December is very cold. Sometimes it is snowing. Have a wonderful tirp! :)

If you want to stay over night, its better to make a hotel reservation. But just for a day trip, the town is open at all time free of charge, as well as parks.

There is no direct way to get there if you don't drive. See below extract from Japan Guide website. By train and bus via Naganohara Trains travel as far as Naganohara-Kusatsuguchi Station, from where there are JR buses to Kusatsu Onsen (30 minutes, 690 yen). The train journey is covered by the Japan Rail Pass, JR Tokyo Wide Pass, JR East Nagano Niigata Area Pass, JR East Tohoku Area Pass and JR East South Hokkaido Pass, but the bus ride is covered only by the Japan Rail Pass. There are various ways to get from Tokyo to Naganohara-Kusatsuguchi Station. The most convenient is by direct limited express train from Tokyo's Ueno Station, requiring 2.5 hours and costing about 5000 yen for the one way trip. However, there are only around three round trips per day. Alternatively, you can do the whole trip by local trains, which takes about four hours, requires a transfer of trains at Takasaki and cost 3020 yen one way. Faster and more expensive is taking the shinkansen to Takasaki and transfer there to a local train to Naganohara-Kusatsuguchi Station. By train and bus via Karuizawa Take the Hokuriku Shinkansen from Tokyo to Karuizawa (70 minutes, around 5500 yen) and then a bus (Seibu Kogen Bus or Kusakaru Kotsu) from Karuizawa to Kusatsu Onsen (80-100 minutes, 2200-3880 yen). JR passes are not valid on the buses between Karuizawa and Kusatsu.

Take train to Takasaki, change train to Naganohara Kusatsuguchi, then bus to Kusatsu