subdomain hosted on WP.com switching to WP.org

I am switching our company blog over to our godaddy hosting account (wp.com to wp.org). It will keep the same URL, a subdomain (blog.ourdomain.com) that is currently cname routed to WordPress.com.

I want to retain the quality link we have established. Have played with the import export and got the hang of that portion of the equation, but I have a few questions I was hoping for some insight on.

1. Once I change the Cname to our godaddy hosting should I close the WP.com subdomain (meaning switch it from the blog.ourdomain.com to blog.wordpress.com).
2. If I ensure the permalinks on the new blog are setup the same as the WP.com blog, will all the links just follow through automatically? Am I missing a step here?
3. I noticed when importing that all the img tags are using WP.com sources still. Is there an import/export work around here or do I need reupload all the images to the new hosting?
4. lastly, this is my first experience with WP.org. I knew going in that certain plugins, themes, widgets, etc. are built into WP.com blogs and not built into WP.org blogs from the start. Is there a list somewhere of these WP.com add ons? Or do I just need to figure all them out through comparing the two?

Thanks for any help.