1) Don't set up a Live account, create a local user account. That way data isn't synced to the cloud like whenever your boss changes settings, downloads new apps, wallpapers and so on.
2) Obviously, set Windows update to only download critical updates, and the optional ones won't be downloaded
3) Travel, Weather, News, Maps, Photos (when you have other albums loaded), Messaging and People will all consume data if the apps are opened and left open or, in the case of News, People and Photos,will load feeds or scroll through photos in your albums, even the ones that are online. You can safely unpin these apps. Photos can be uninstalled, but Messenger forms part of a group of apps that are available from the store as a single download, so uninstalling it will also take away Calendar, Mail and People.
4) Any app downloaded off the store that has an online component will need internet access, but only when its opened. Apps that don't incorporate some kind of feed won't consume data at all, and some apps even cache their feed.
5) You can't restrict updates of apps. These updates are fed to you through the App Store and there's a little number notification to show you how many updates for your apps are available. You can choose to ignore these updates, although it may be the services are impacted
6) Windows 8 also has a nifty built-in data counter accessed through the Network counter that lets you know how much data you've consumed during a particular period. This counter counts for both upload and downloads and can be reset at any time, say at the beginning/end of every month for more accurate data control.
Other than that, it behaves exactly the same as Windows 7 with the same settings and Microsoft Security Essentials installed. If your boss uses Office, the 2010 or 2013 versions come recommended, although 2013 ties better into the Start screen and the rest of Windows 8. I'd also like to add that when Xbox Music and Video launches in SA, your boss would do well to use a Wi-Fi hotspot or data off an ADSL line lest he chew it up too quickly.
