Right off the bat, my apologies if this has already been suggested.
Just wanted to say that I've absolutely loved the game so far. As a lover of the original games, divinity, and a regular d&d player, this game has lived up to my high expectations

My suggestion is that letters and books be kept in a separate part of inventory (maybe global, and maybe having no weight component). For myself personally I enjoy reading books and letters for flavor, but it is a pain having them cluttering up your inventory. Obviously there are solutions (not picking up books, putting them into chests in camp), but in my view that's an unnecessary hassle. Personally I think that books should serve the purpose of fleshing out the lore for those who are interested, so if you create a system where books/letters have their own spot, don't take up weight, and have no resale value you can make life a lot easier for those who are interested in following those threads.
Just a thought, and again great work so far!