Togendai to Shinjuku on Okakyu Highway Bus?

I'm intending to head back to Shinjuku from Togendai (in Hakone) using the Hakone Freepass on Odakyu Highway Bus. Is it possible? And I think I need to pay extra 850. If yes,
- What's the last bus from Togendai station?
- How long would the ride back to Shinjuku?

If no, if I have to ride to Gotemba Station,
- How long would it take from Togendai to Gotemba?
- The ride would be covered under Hakone freepass?

At Gotemba station,
- What is the last bus to Shinjuku?
- How long would the ride take from Gotemba?

Thanks very much!

I'm intending to head back to Shinjuku from Togendai (in Hakone) using the Hakone Freepass on Odakyu Highway Bus. Is it possible?

yes.

And I think I need to pay extra 850.

Yes.

The rest of your questions are answered by the bus' official website:
http://www.odakyu-hakonehighway.co.jp/common/pdf/english.pdf