Yes they will get your tweets. It will appear in their @replies tab.
If they are not following you it will not appear in their timeline. It will always appear in their @replies though.
To post replies to someone on twitter, you simply put the @ sign before their username. For example... @efink101 hey how are you? Simple as that. :)
While you can only "direct message" people on Twitter who are following you, you can try to get someone's attention by referring to their user name and adding the @ symbol prior. For example @DavidWallace which is my Twitter user name would show up in my "replies" box in TweetDeck which is what I mostly use to access Twitter.
A 'private' message that doesn't appear on any timelines. You can only direct message someone who is following you.
Yes they will see it in their @replies.
yes
It is impossible to send a DM on Twitter to someone who isn't following you. The user has to follow you before you can send them a DM.
You can block them - you won't see any of your tweets when you do.
Yes, anyone who is following you when your tweets are private can view them.
At the top right hand corner it tells you how many people you are following and how many people are following you. If you click on those that are following you, they are in order of when they started following you. So, the one at the top is your most recent follower.
I think you can follow someone on Twitter if you have 900 K people already. It should not matter how many people you are following or who is following you.
It means "Someone I'm Following"