so what do I need to do so that all my things and traces of all activity are wiped from the laptop
Safest way is to physical scrap the hard drive with a big hammer :0)
and take it back to a factory state
buy a new drive copy the restore partition from old drive to new and do a factory restore.
If you don't want to go that far do a factory restore and the download and install CCleaner and use the "wipe free space" tool (7 times) to clear everything else from the drive your data will unrecoverable unless you have CSI tools :0)