First you should make sure you are having that many people at your affair. (Or someone is gonna get tired of eating coleslaw.) If you have the number one of people coming then allrecipes.com is a great place to start.
If you do not have the number figure on 3/4 of your guests will arrive. That would be about 150 people and you should have a half cup per person. So you would probably be looking at 10 heads of cabbage easily.
Also another factor is if you are cutting it up small or leaving it in chunks. Larger chunks makes it look more and of course smaller, small.
Check out the recipes at allrecipes.com. They have some wonderful recipes.
Good luck to you.