In this interview, in 7.40 the interviewer asked Swen Vinke about the origins stories in DoS2 and if they will make a comeback in bg3.
https://www.youtube.com/watch?v=M57vTyM-iE4Swen answered (loosely translated) " It´s a system that will evolve. One of the things that they focus on is the party and personal stories. It was explored [in DoS2] but it was not really explored as I would have wanted. In this game, Gather your party will be one of the pillars of the game. The party will be important. Party will be important but also the Hero
[singular] . Each Hero has the story of their origin if you choose that but you can also obviously make your story anyway".
He also repeats that will be based in D&D 5e, and it would be faithful to the tabletop but since it is a videogame some adaptation would be needed. No further details on combat.