What are the best sources for information on Realms deities?
All of your questions are answered in the three-volume series, “Faiths & Avatars”, “Powers & Pantheons”, and “Demihuman Deities”. While these are second edition books, much of the information is general and can be applied to a third edition game as well. F&A details the major deities worshipped in most of the lands of the Realms, and P&P gives the demipowers, as well as some more obscure pantheons. DD details the elven, drow, dwarven, halfling, and gnomish pantheons.