1- i have not idea ot this
2- as far as i know you need a commander for each nationality, in example, if you defend paris with a mixed force of germans and italians you will need a german and an italian commander, at least, my gaming experience does show this way, i do defend paris with mixed force, better german commander, but i do know that italian units are not getting the better german commander's bonus.
hope it helps,
with best regards,
There is no plan of battle that survives the contact with the enemy.