Hey Hope,
Thanks for reaching out to us!
Sure thing, you can query events from across your whole network but like you said, it could become a really intense database hit depending on the number of sites and the number of events. You could skirt this a little by only running the query on occasion and caching the results so it isn’t running all the time.
An example approach that you could take would be something like:
https://gist.github.com/BeardedGinger/1a1e16f3fc828666dba31ed417b69ecd
Let me know if this helps.
Thanks!