I waited until I finished the story to do free roam, but you should be able to just do it. When you jump off the helicarrier, just ignore the little red guy you have to follow and do free roam. But it's better to just beat the story first.
You need different characters to do different side quests. The story is only about 8 hours of play. If even.
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.