I have some ideas, and I'd be fascinated, but the big thing is the differences between the books and the movie. R in the books is older, a bit more pretentious?, and has some different opinions and tastes in comparison to movie R. I use the books to help flesh out a lot of the world building aspects, but haven't incorporated as many of those differences aside from some personality quirks.

I've kept the concept of R's backstory very vague. I have general headcanons (I think he was in college, I think he was a bit of a nerd, I think he had a rough home life and craved affection and companionship) and let those lead me. In The New Hunger, Marion heavily codes R's death as a birth and I like that angle. He's still new, and fresh, and a clean slate. He's learning and exploring. He has a personality, but he's malleable because he hasn't had many interactions or experiences to shape him.