Is it possible to change the AI behaviour for party members post creation? I am not sure I want to pick both sides of the dialogue in every interaction, and kind of want to be surprised now and then. IF not then it isn't a big deal to restart (I just started the game)

Yes, after you find the third star stone and open the inner chamber portal in the homestead.

Ah, so it won't be for a decent amount of time then

You can get 2 star/blood stones within Cyseal, and it is relatively easy to get to another north east of town, if you sneak past a couple opponents in the fire area (from the gate by the legion headquarters, head north, then east slightly, and send one character northeast carefully).