Some of this is easy -
1 - single login system between vbulletin and front page of blog. This is heavily documented at vbulletin.org
the process must be like this:
when a post is created on movable type a thread will be created in the forum and the thread id retained.
Any existing posts in the thread will be shown at the foot of the article.
Any new post made on the blog will be added to the vbulletin thread.
Users can also access the thread externally