Thinking about this topic i came up with an idea:
I was thinking that what if the nation that built the port always gets to use for the bonuses of nation titles(captain, major, etc, except governor.) even if the port is taken over by another nation.
Captain blue wrote:50-70 is a little to low to start your own port.... around 100+ it should be..... IMHO this is a good idea but i don't see it getting implemented
How about 80-100 than whatever you want to invest, that way it leaves a little legroom for your population increase.