1. Yes.
2. Whatever you want (anything legal, anyway... no splicing different dialog together to make bomb threats, etc).
Before release the beta for Dragon Commander explicitly had no NDA, and there are already lots of pre-release / release videos around (though most were focused around the release, so there are not a lot in the latest version).
3. I believe Youtube wants a release form for use of game video if the channel is monetized. AFAIK Larian has not posted a general release form, so try emailing support@larian.com.
