You cannot see who is following you on Twitter.
If your account is suspended on Twitter you cannot see your followers or those you are following.
Yes, you can see how many people are following a Twitter account. All you have to do is go to the person's profile and look at the "Followers" amount.
No they won't see your tweet.
If your tweets are protected then only people following you can see your tweets. If she isn't following you then maybe she has access to an account that is following you.
See Kourtney Kardashian Twitter account here @KourtneyKardash
When you lock your Twitter account only your followers can see your updates. Also, you will have to approve any new followers. It's like as if only your friends have the option to see you, kind of like being a king, you approve and see who can do stuff, but only a few people can see you.
See the related link below for her Twitter account.
Yes you can cancel your Twitter account. See the related question for how to do this.
See the related link below for his Twitter account.
See the Related Links below for the link to David Henrie's Twitter account.
See the related link below for his Twitter account.
You can use TwitPic (see related link) and sign in with your twitter account.