I agree with moo-juice, the correct approach would be people + roles. Here's a concrete example.
I would take a single table with empty username/password columns over a separate table. I would introduce an additional table called roles or some such, and another linking table that linked people to what they are (A user, a customer or even perhaps both).
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.