By "a new board" do you mean a new forum? If so, only users subscribed to the forum will be notified of new topics posted to it. So, if you create a new forum, users will not be subscribed to it by default. The only way they will get notified of the post is if they are subscribed to all new topics across all forums (and that is typically a more rare scenario).
There is no way to completely prevent subscribed members from getting notified of a new post, though.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .