Just a friendly word of caution:
if they don’t appreciate what you’re telling them to do, … and if the minis you’re building fail to do some magic data protection that they / you hadn’t thought about… it’ll be your “fault”
They need to take some ownership



Look into radicale if that’s you’re using NC as a DAV server - and everyone’s using their phone as a client
It’s so simple & lightweight (but admittedly the webgui is admin only - no visible calendar)