First question - you build the cities so in essence you could build them anyway you want too. As to what way will be most beneficial / efficient that is unknown.
Second question - as for the bankers and diplomats/kings etc they haven’t stipulated a job list yet i have been waiting to see one personally. but giving a unit a tool in combination with skill ups/levels makes them said class.
Thrid question - this should be completely possible with the modability that will be in game.