I have done a lot of drives with 10 to 15 people. You can get away with 1 or 2 beaters if the block is small or you have dogs, especially fox hounds. A fox hound barking upwind will usually move all foxes winthin a km or more. All you then need is enough shooters to cover the escapes, if the foxes dont get through you have enough.

We had a lot of beaters because it was a club shoot and we had a lot of shooters. The shooters and the beaters rotate so everyone only has to walk (beat) once.