All the diary entries, the letter writing, I assume all that stuff can be easily dealt with. This will have an epic scope, from the Civil War to WW2 or thereabouts.
Robinson is a national treasure. I'll tell you this: she's never just screwing around; she's trying to hit home runs every time up. I don't know how many people have read these books, but i know some people that have, and find them pretty overwhelming. It's not surprising to hear that Scorsese is a fan; it fits completely, the mixture of violence and religion in so much of his work. And DiCaprio is going to be John Ames; ok.
You can usually find Gilead and Home near the top of most lists of the greatest novels of the 21st Century. Scorsese loves these literary properties. Several of them have obviously resonated with him (like the non fictions Killers of the Flower Moon and The Wager). I hope he does this proud.