What type of game? A mobile game can be as few as 1-2 people, while a current gen pc/ps2/xbox title can vary from 20-80+ depending on budget, impact of title etc.
Again, skill requirements are also somewhat fluid. If you are doing 2d mobile games, you will need pixel artists, not 3d modellers. How quickly and how do you intend bringing a product to market – this will affect a sales team/marketing requirements.
A little more specific would merit a more detailed answer.
Dave