my approach to deciding is quite different than yours but i only play as the romans so here are my rules:

Once they come to age, all family members are sent to Roma. They work up the Cursus Honorum on their own. Once a family member attains the Ex-praetor trait he is either shipped to govern a province or if he has good command traits then he goes to lead an army.

i might send out quaestors to govern provinces near rome for the duration of the quaestorship. I like to do that and role play the fact that they are raising an army when i need one by grouping all the units in this province when i am hiring.

If Rome gets crowded (and it does) then I send family members that are 30+ years to Athens to continue their education.

There are two governs in Spain, two in Gaul, one in Italian Gaul, one in Sardinia, one in Sicily, one in Pella, one in Italy and sometimes governors are sent to troubled provinces to keep them intact.

Generals retire at the age of 60. Usually, I ship them to Rome for a year or two then send them out to govern a province. 60 year old governors rarely come back from their retirement provinces.