The number of interacting participants verses participants in my large SSO-gated community, hasn’t reached the level yet where this would be an issue.
I couldn’t find documentation confirming that closing an event stops edit notifications for users marked Going. The documented setting is discourse post event edit notifications time extension, which refers to notifying Going invitees about edits to the original post, but I couldn’t find anything specific about how Close event changes that behaviour.
Sources: Discourse Calendar (and Event), Creating and managing events