There is no FTP access to free hosted WordPress.com blogs and we bloggers cannot install any plugins. To have plugins and Google Analytics you need to hire a web host and set up your own self hosted WordPress.org install. http://support.wordpress.com/com-vs-org/
Advertising outside of WordAds at WordPress.com is not allowed.
There are no restrictions if you setup a self-hosted WordPress.org blog instead of a WordPress.com blog, but there are some added responsibilities.