If you're going for an achievement, you should stick to what you've already put the work into. I don't know about the specifics of the achievement, but if you've already collected all trophies and riddles, then your Story+ WILL NOT have anything to collect. You still have to do the side missions again, but no riddles, no trophies.
Even if you didn't collect everything, Story+ will remember which ones you have gotten, leave them out and only what you havent done remains so you definitely don't need to get them all in the first playthrough, and no duplicate efforts riddler wise in the + mode except saving hostages. A very big upside to Story+ is it is definitely harder. Easy may still be easy, but it won't be nearly as easy.
The blue flashing counter-indicator also is removed, and enemies are given weapons earlier, more of them, different combinations of thugs, etc. Just cant promise your easy save will count towards anything you do on a normal or hard save, and vice versa.
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.