Hi, Erica.
We’ve heard of some sites running 10,000+ events, but the Events, Organizers, and Venues are just WordPress custom post types. We’ve also heard of others’ sites struggling with just a couple hundred events.
With any large scale WordPress site (i.e. lots of posts or lots of traffic or both), you’ll need to have things setup to handle the extra demands.
We do have his article that may help: https://theeventscalendar.com/knowledgebase/performance-considerations/
Also, you could implement some cleanup routines to auto-delete events older than a certain time period. We already have this as an option for PRO’s recurring events functionality (the default is 24 months) but it doesn’t delete events that aren’t part of a recurrence series.
Please let me know if you have any follow-up questions on this topic.