Dom, there are others on this Forum, such as Hook, who are far better qualified than I to answer you in full but this is what I understand.
Currently AI has the same program for the French and the Allies, although I have seen the Austrians attacking in massed column. You can change the way AI reacts for diferent armies and types of unit in the Doctrine Editor. This in essence, makes the AI customisable. I also know from discussions on previous posts, that AI will be programmed for the Brits, when that expansion arrives, with "Reverse Slope Tactics". Finally the smallest unit you can command is Regiment, however you can deploy skirmishers from an Infantry regiment.
Hope this helps