If you intend to use W-8.1 as a desktop computer interface, like W-7 with 2 simple clicks in the "Taskbar Navigation tab" you can have W-8.1 open directly in the desktop mode instead of the tiled UI. That alone saves time as well as data usage.
There was an additional update to Windows last Tuesday, only a little over 5 MB.
Quick Time had about 44 MB Your virus program undoubtedly downloaded updates a number of times and the browsers had some update activity.
Even though you have most things set to manual you would be surprised at the activity going up and down in the background. If you haven't installed a Usage meter on your pc yet you might want to try something like "Net Guard" which is free and will give you an indication of what programs are using the net and how much. It also can give you a .pdf report of any period. I've used it for over a month now, thanks to Gwalk's suggestion, and find it very useful. It does report back to the vendor but uses very little data allowance to do so.