This is a situation I'll be facing soonish.
My modus operandi will be:
1) Arrange domain and hosting.
2) Install wordpress
3) Article by article, move the content to wordpress.
4) As the article is generated on Wordpress, leave a link to the newly created post/page, with a message that the content has been moved.
Now, Blogger blogs, as far as I know, don't really have a page rank as such, so, That is not a problem. If you have followers, let them know well in advance that you're moving.
By moving your content (DON'T just copy it. Copy it, and then delete it.), you won't have any duplicate content hassle.
Oh yes, moving to Wordpress is a great move. WP3 is great. I use Blogger at the moment to define what direction my WP blog should take.