Hi there,
You're right, you cannot host AdSense, that requires our VIP level service. However you can opt in for our WordAds option if you'd like, which puts our normal ads on our site, but does revenue sharing. For more information, you can go here:
http://wordads.co/
In regards to your question about moving to WordPress.org, if you're interested, we offer an upgrade called Guided Transfer (available in the Store section of your blog's Dashboard) where we take care of everything for you: http://en.support.wordpress.com/guided-transfer/
Otherwise, you'll need to install WordPress from http://wordpress.org/ on a hosting provider. We have some recommendations on hosting providers at http://get.wp.com/hosting/
Once that's done, you can move your content following this guide: http://en.support.wordpress.com/moving-a-blog/#moving-to-wordpress-org
WordPress.org has complete support and documentation sites for self-hosted/installed versions of WordPress at:
http://wordpress.org/support/
http://codex.wordpress.org/
About that VIP level package that I mentioned, we do offer yearly and one-time premium support packages for WordPress sites through our VIP program, available at http://vip.wordpress.com