I've booked a 'Single C' room, which is their cheapest room at 10,000 yen per night. How small of a room should I expect?

This at least looks like a decent hotel. I'll only be staying there for one night. My trip is 6 nights in Tokyo (at the Hilton), then 6 nights in Kyoto (at Rhiga Royal), then 1 night in Tokyo before heading back home. I just didn't want to have a 24+ hour day of travelling without the Tokyo stop, but didn't want to waste a bunch of time getting to my hotel. It sounds like I'll arrive from Kyoto on the bullet train at the station, and can take the Narita Express back to the airport from there as well.