We have 10 000+ events(no joke) and it is still easy to manage.
For every Layout we have 1 eventsheet (14 actually) and for every bigger functions(like viewpoint functions or often used family/image management) another event sheet which gets included every time we need it.
The eventsheets are grouped up by objects/functions.
Eg. The player or the top bar is a big part so we create an group named "player" includes the groups "functions", "control or handling", "effects" and so on and every group includes more specific groups like "Creation" or "Attack".
This makes it for us quite easy to manage and every team member can easily find what he searches ;)