Having played this game for only a week, and through trial and error of learning the game on the fly, I have come to a conclusion about the AI setting.
First thing is to use FOW for yourself, but allow the AI to see everything. This has led to proper gradual buildup and response from the AI to my movements. I leave winter attrition above average and I allow the AI +2 on detection.
I am a huge fan on the FIW, both the game and the history. The difficulty of supply, movement, winter, and increasing British resources create authentic historical challenges. I am quite the Frankofile, So the moment Montcalm is on the scene it is off to organize the Regulars for an assault on Fort William henry followed by a push to Albany.
You can do this sooner, but you can also get quickly countered and retreating with winter setting in can be a disaster. Best to wait until the master is on the scene.