Intermediate starport strategy question

Starport output is linked to the number and type of factories, the proportion of your spending going into military production, your overall spending level, asteroid base output (if applicable), and planetary focus spending.

Each starport is independant, at least in terms of affecting what the others do. Global factors such as military spending will affect all of them equally.

All production (social military and research) is independant of population.

You forgot about Economy Starbase modules. If a planet is within an Economy Starbase's area of effect (and that starbase has Manufacturing modules), the Starbase also provides Military production for your planet/planets within that area of effect.

Hope this helps.
ROCK ON!!!