The Chromebook management console offers policies to enforce a proxy,
or set your own URL whitelists and blacklists -- which method you
choose would be dependent on how much you want to block, and whether
you want to use a third-party filtering service to do it.
The management console also allows you the ability to pre-install
applications/extensions from the Chrome Web Store. (Most applications
are "freemium", so you can install and use some basic level of
functionality for free, but if you want the paid version in bulk,
you'd need to discuss with the vendor.)
Check out more info about the management console at
http://www.google.com/intl/en/chrome/business/chromebook/features.html
(do a quick search for "management console")
Hope that helps!