I don't have exact numbers, but I am using 75 fatigue and it has been solid.
I see no real "robo QB" with the complete opening post setup. Really, the only QB that seems to put up crazy numbers against me is Brady, and that is ok with me.
No, as long as you don't have control of that team as an owner or coach (no idea about player) the CPU seems to use whatever autosubs the user team has.