So it’s likely that I’ll have 2-5 people accessing the central info.

It’s one household so they’ll be on the same network but ideally I’d like to be able to sync calendars (and the associated info) at any given time online.

That’s where I run out of knowledge, essentially. Setting up a basic CalDAV server (like Baikal for example) isn’t beyond the realm of possibility, it’s just knowing how to actually get it online.

Would I need my own server in my home, or can I host it similarly to my Wordpress website, for example?

Yeah, CalDAV looks like the best fit from my limited searching, it’s just actually putting that into a usable system that I can use that I’m struggling with!

I don’t mind a bit of proprietary-ness, what I’m after is controlling how and with whom I can share my data.

Essentially the goal is to have a family’s worth of accounts with Calendars, To-Dos/Reminders, and Notes that I can back up myself but still allows syncing to phones/PCs, etc. and basically a central calendar for ‘global’ (ie. Whole family) events.

33 here - if the staying up is enjoyable then 1-3am is fine. Hangovers are worse than when I was 23, but I’m usually back up to speed by lunchtime.

Of course this is heavily influenced by how much water I drink while I’m out. Hydration is important folks!