You kinda lost me with the word "backstory". I love backstory and think it's great for characters to have... in a tabletop game run by a human DM. There's no limits to human player creativity, but in a videogame, everything has to be put in by hand. There simply isn't going to be the same amount of reactivity and story integration to do more than a fraction of the possible ideas people have in their heads for a backstory.
All that sounds like a tremendous amount of work which will nonetheless leave a lot of players unsatisfied because they couldn't make the backstory they had in mind. It's better to try and accept the limits of the medium and have the resources which would have been spent on that directed elsewhere.
