Let's compare ZAMS stars with different mass and equal composition. Higher mass might produce higher central density (and pressure) because more gas is pulled inwards and compresses the center. But this seems to be simplistic: very low mass stars have an electron degenerate core and are fully convective, which isn't true for heavy stars. The temperature profile in a massive star isn't the same as in the Sun. Assuming constant density throughout the star gives an equation for the central density depending on the mass, but the assumption isn't realistic. So it isn't obvious how the central density depends on the stellar mass.
(1) how does the central density depend on the total mass for ZAMS stars with the same composition? Is the relation monotonic? A diagram would be welcome.
(2) is the relation between central pressure and total mass the same as for the central density?