Let the subject matter determine the length of the video.
If the subject matter is only worth ten minutes, do a ten minute video.
If the subject takes an hour, do an hour video.
Please do not split up a video just to have three ten minutes video, where one thirty minute video would do just fine.
Right. However, if someone is going to cut them up post them ALL at once. Whatever you do don't post ONE per day. This will gurantee you get less views of that video, and also less viewers in general on C9.