Thanks JustinG both for your advice and taking the time, I think I will re-assess my desire to use metadata for this and stick with items. The upside is less work as it’s a more straightforward port of what I have in OH2.x.
FYI, the Habpanel issue I was referring to is here [SOLVED] HABPanel sluggish and is basically that, especially on lower powered devices, habpanel takes a while to load the items as it loads ALL of them, not just those on the page, it can also get overwhelmed by the number of events. A forum member posted an addon to strip items and events that are not used in the panel to improve performance, which I’m using, but its still not great on my old wall panels (ipad air 1’s). OH3 may have improved on this, although I see people are still finding a need for it based on that thread. I’ll see how I go. I have a few thousand items from memory (about half due to the lighting) and quite busy events with lots of chatty devices.
Early days yet in exploring how OH3 will work out for me - I’m finding the learning curve surprising steep considering I’ve been using Openhab since V1, perhaps as I’ve been file based the whole time. I want to try the “new” way with the UI this time though, but for some reason I’m finding the UI quite unintuitive despite the doco. Maybe my brain is just not wired for it. I suspect once I get the hang of it I’ll love it.