if you think thats all that you need to do to stop activity tracking and information gathering then i really dont know what to tell you
Cortana stores every single thing you do, from web searches to the programs you download, in an online cloud that Microsoft has access to. You can even clear the activity that has already been recorded after you turn cortana off.
If you're super paranoid you can even turn off location, privacy, and advertising settings. With some tweaking you can have as much privacy as you want.