Lakeside55 wrote: XAMPP is not listed in the Programs from the Start menu, or among the program files probably as I installed it into C:
Thats completely normal if you imagine that you just unzipped it, like a portable app. You don't downloaded and used the installer version.
Lakeside55 wrote: Also, when I start Apache (briefly as it's probably a security risk) it does not show up listed among the 'services' from control panel.
That's normal too. you did not register any services for the components. You can do so (and it is recommend at least for mysql/MariaDB) by running the control panel with enhanced administrator rights (rightclick -> run as administrator). After that you can see red X buttons next to each application you can click to register the service.
They behave like any other automatic windows service (will start with any system start for example).
Eversy program that runs on a system can be a security risk, especially if it opens a port and very important true if the system is reachable from outside of your protected home network.