1 guy: totally insufficient for the amount of work required to make a burger
2 guys: fine until something inevitably happens and they draw a tape line down the middle of the kitchen because they are no longer talking to each other
3 guys: one guy will inevitably be "the third wheel"
4 guys: the number 4 is considered unlucky in Asian culture
5 guys: perfect
6 guys: will be too tempted to quit making burgers and go play 3v3 hoops