The theme doesn't have anything to do with the functionality, ease or difficulty of the blogging application.
Are you asking how easy or hard WordPress is to learn as opposed to Blogger/Blogspot? If you are comfortable with Blogspot/Blogger, then set up a self-hosted Blogger blog.
If you want to "testdrive" WordPress, sign up for a free WordPress blog at http://www.wordpress.com
Live with it awhile and decide if you like it well enough to invest the time it will take you to learn it (it's different from Blogspot for certain).
But I now think you may just be asking how difficult it would be to port your DESIGN to WordPress. It's not hard at all if you understand a bit about CSS and HTML already. The layout of your current blog is a simple one (that's a GOOD thing). So you could probably start with the Classic theme that ships with WordPress.