Is it necessary to install app updates listed in the Store for performance or security reasons if I'm not actually using any of them, aside from having their tiles on the Start screen?
You don't have to install any app updates if you do not wish to, but it is recommended to do so for security and bug patches to keep them running properly. You could disable automatic download of Store app updates to prevent them from being updated until you manually update them.
I kind of like having the default apps just for their tiles on the Start screen, but I don't actually use any of them. I'm just wondering if I need to bother updating them every time there's an update if I'm not actually clicking on them/going into the app...