So my questions are as follows:
1a) Will there be an AI system for each party member, and how customizable will it be (I personally felt that IWD 2's AI system was the best from those listed above, it offered a variety of choices without me having to pick individual triggers for each action).
Yes, it's called "co-op buddies". Not as advanced nor customisable as Dragon Age: Origins or Pillars of Eternity2 but it does the job. Turn processing time is annoyingly long though.
Joking aside, I doubt something like that will be in. I have never seen a turn based game, which would play for them.
