Night train Tokyo-Sapporo/ Sapporo-Tokyo

Hello! We plan to visit Sapporo a couple of days from Tokyo in November. We have some doubts:

1) Does the night train operate every night? Does the service go back from Sapporo to Tokyo also at night?

2) Are the extra fees mandatory? I know there are beds, but is it possible to sleep in the seats without paying extra? We are not looking for luxury, we are looking for the best way to reach Sapporo without wasting daytime on a train.

3) If all the above is negative, where can I check the timetable of the trains so I can find the most convenient trains?

Thank you very much in advance.