Concerning touchscreen: there's the Estouchy Skin for Kodi Kodi Community Forum - Estouchy - I have to admit I never tried it though as I don't have any touchscreens.
You can disable various main menu entries (like Movies, Videos, ...) in Kodi if you don't want/need them - just head to Settings -> Interface -> Skin -> Configure Skin...
If you want some extended functionality in Kodi you'll need to check if there's some addon readily available that suits your needs or create a feature request for Kodi if some core functionality needs to be extended.
LibreELEC is already quite stripped down but if it bothers you that some background processes like pulseaudio, eventlircd, ... are running and you don't want/need them you can simply disable them via "systemctl mask SERVICENAME". A while back ago I did that to repurpose a Wetek Play 1 running LE as a headless tvheadend server - I even disabled kodi as it'd consume a significant amount of CPU and memory when it just sat there being idle.
As all of these are just configuration changes you can easily check yourself if it brings you nearer to your goal. If you discover that's a viable way to go and you want that config "out of the box" then you could start thinking about creating an LE community build or fork that ships with these changes as default.
so long,
Hias