(Not a Teacher)
That's a lot of questions for one post, compadre. I'd advise you to break them up across 3 or 4 separate threads. Here's my opinion on your first two questions:
1) All of your answers work. I wouldn't use 'shall', however. It sounds a little archaic. All of them are valid responses to the question "When are we going to start?", though some apply in other contexts, as well. For instance, if someone asked me if he had time to use the restroom, I'd be more inclined to use the 5th or 6th response in your post. They both emphasize how close the start time is.
2) Again, both of your answers are fine. I wouldn't say the first response is 'neutral', especially if you put stress on 'will' as you say it.
- For Teachers