When you have 5000 friends, any person who tries to accept an invite will get a message of "This person has reached the friend limit."

You can have your FB account closed for being too spammy, meaning if you constantly invite people to (obvious) spam groups or if you send out 6000 events in a day.

In my experience, it's best to have two types of FB accounts: Ones that are the sole creators of groups/events, and ones that have 5000 friends that invite people to those groups/events.