You can see all your commanders and provinces in Nation Overview screen (F1). From there you can select provinces (the game will close that window and center on that province), change taxes and defense from there without going on main map (fastest way of doing it), see all the details about each province like population, resources, supplies, used supplies, unrest level, what level and type of mage has searched for magic sites there, etc. You can see the list all commanders in each province and access their info from there too, and if you get lots of provinces and commanders you can press TAB key to hide commanders for better overview of commanders. That screen is shamelessly useful and it will become your best friend.
