Mike,
Glad to hear that you are going to use WP for your main site. Its a good decision, I don't think you will regret it. You should not need to register an account to use WP. Just download the software and start working with it.
No need to transfer your domain either, if you are with a good host, you should be fine running WP on their servers.
I would build the site on m,y local computer, then when it was ready to go, upload it and import the database on your live site. I have a tutorial on installing WP on your local machine: http://xcartguru.com/tutorials/wordpress-tutorials/installing-wordpress-on-your-local-machine/
You can also build it "in the wings" directly on your live server, just set it up in a subdirectory or on a subdomain while you prepare.