I did not read everything above, so here are my 2 cents about origin characters:

I play the game with my custum char and consider the others as companions in the same way as BG1+2 or many other games.
This way it feel like playing any other RPG and my companions seem to be more reactive than in most other games which is good.
By reactive I mean comments, suggestion or they like/dislike my actions when I talk to other people or do stuff.

There are 2 problems, at least for me who plays single player only:
- NPC tell the same stuff again when I talk to them with another party member. This can be irritating when you (the player) think: Why do you tell me that? I already did this.
solution: always talk to people with the same char, usually the one with highest charisma and talking skills.

- If your custom char is not the one with highest cha you will usually talk to NPC with another char, This means you are role playing someone else.
solution: Talk to NPC as your main char and role play someone who may be very strong or clever but not the best talker.
OK, this will be hard for me I admit.

groovy Prof. Dr. Dr. Mad S. Tist groovy

World leading expert of artificial stupidity.
Because there are too many people who work on artificial intelligence already :hihi: