Well I don't think 40-50 servers Pete, maybe 1 server per 2 tables. That's still plenty of servers however. Anyway to give you some kind of idea what goes on, and maybe raise the level of respect for professionals who do this on a daily basis, here's a brief rundown of a little part of the operation:
1) You will not be doing prep for a week. Rather, you better be prepping a little the night before and most of it the day of to ensure high quality.
2) If you are serving a protein portion, this will need to be marked or browned, put on sheet pans, chilled, and cooked until done about 30 minutes before service. 400 will require between 16 and 30 sheet pans depending on what you're doing. Less room required for filet mignon, more for ribeyes and full breasts. This requires of course rack space, so about 4 bun racks (or speedracks depending on where you live) and a walk in cooler to chill them.
3) Cooking. You will need at least one shelf oven. Two if you want to get plating done in less than a half hour.
4) Plating. You will need room for plates and space to set up your plating line. You can make four stacks of 100 plates each and have one person do one thing, or about 16 feet of linear space if you want to do it assembly line style. One server will be removing the plates and putting lids on them, and one person stacking them on the tray. One experienced server can carry 16 plates. If you don't have the room or the people then you will need three food warmers. These are boxes which you plug into the wall that keep food warm. Once again you plate, you stack, and you store. When it comes time to serve you pull them all out of the warming cabinet and go 16 at a time.
I haven't even yet mentioned dishes, salads, water, wine service, cake cutting, veg and starch, setup and teardown, or hiring temporary staffing, location, possible offsite license, etc.