That would be a long answer.
To many factors involved but figure feeding 5-10% of that number.
If you can cook, hold and serve that many you should be able to handle it.
If you only have done small catering gigs i'm guessing you never been thru a HD inspection so lots to learn.
Check this forum for lots of good threads on these subjects.
Pitmaster @ Lockharts BBQ
I cook the best brisket north of Dallas. Get over it.
Northern midwest director for OBR
BBQ Person of the Year 2013