The Papermaker bonus is +2 and free maintenance. The 1/2 per citizen is a standard Library effect. I arbitrarily chose 6 (3 ) because it is realistic to get this population at the point in the game where you have constructed the three buildings (and possibly some units as well). If anything it skews the Pyramid benefit, because +2 is a bigger bonus (percentage wise) in a smaller population city. All three remaining buildings really scale well to a wide expansion strategy.