Do you mean the FR Faiths and Pantheons book? Because SCAG already does that. And there's a PoD fan one on the Guild:
http://www.dmsguild.com/product/243212/Faiths-of-the-Forgotten-Realms
If in general, I'm uncertain what has not already been said.
Yup. Have all of them. For inspiration and background they are great. I think OP is looking for an official WotC book updated for 5e so they don’t have to come up with their own adaptation. Everyone plays a little different. All good.