We were 1E/2E players. We did that plus henchman. And as for backstory. It either unfolded throughout the course of play or u had none. In any game I played players did not give the DM a complex background or much of one. It developed or it didn’t.Curios, did you ask for player buy-in for that many? When the DM needs to divide their attention that many ways, work in character arcs for that many characters, when combat is soooo long between actions. That impacts them greatly as well.
I probably would have skipped on a 12 player game.
the most complex background was I am from specularum or I am from minrothad. And then I worked with that if it was important.