Industry sizing recommendations are that your salt chlorinator has 1.5x to 2x the capacity of your pool, so you would likely want the next size up. More sizing information here. The settings are unique to your pool's use, climate, chemistry, etc... but once you get the system set up you do not usually need to make frequent adjustments to it. Salt is not used up during operation and doesn't evaporate, so after the initial install you only usually add salt seasonally to compensate for rain, splash-out, or draining of the pool.