I’m down with these choices except for Maggie Smith as Fairy Hardcastle. It should be Pam Ferris (Miss Trunchbull from Matilda) or Kathy Bates. Somebody big and burly.
What? You’ve not read That Hideous Strength? Well, first you need to read Out of the Silent Planet and then Perelandra. All great yarns. And That Hideous Strength is a sort of novelized version of The Abolition of Man, another book well worth reading.