Prisonchef has many great points and ideas, and jimeats has some good questions that need to be considered. I too, have done some large catering events. One was for George Lucas in a major convention hall, complete with Stormtroopers and other Star Wars characters promoting upcoming merchandise.
Another and very memorable affair was in San Jose, at their Museum of Art, over 50 miles from where our company was located. This was an Egyptian themed affair complete with slaves bearing the queen carrying a albino python. The thing about that party was that we discovered that we did not have enough shrimp and oil for the deep fat fryers. Fortunately I knew of a local and major food distributer that managed to bring the required missing ingredients to us and it was a success.
I am not writing this to brag, but catering is one of the most interesting culinary jobs, every day is different. You need to be able to plan and adjust to what wasn’t forseen.
You do not say if this is a seated affair or buffet. This is important. If you have 50 tables of ten people, just getting enough servers to properly deliver hot food to the tables is a challenge. The last table to be served will get their meal as the earlier ones will be sitting waiting for the dishes to be cleared… and where is dessert?
Please write back with what you are planing to serve, what equipment you have available, staff, and are you capable of doing. Pre-prepping is essential.