Have you read The Art of Animation by Bob Thomas. It's a nice insight into the early years to present. There are currently 3 editions available, one which goes up to Beauty and the Beast and the updated one which goes up through Hercules. There's also an interesting series available on Kindle called The Vault of Walt. I think there are 5 or 6 in the series now. They give a lot of background on a lot of Disney history from attractions to movies.