Hmm, to me, the most important element of a fantasy story would probably be the concept and the world you would be making. Take Harry Potter as an example; J.K. Rowling created a lot of specific features like every detail of the creatures, the spells, the structure of the school, the characters, and the world she made. She added tons of little details that connect to the story, but she also had to make sure that the readers/watchers would be able to understand the aspects she has added.
Since you have already defined the races, the settings, the religions, and a bit of the magic systems, I think you should focus next on the tiny details that would build up and support your whole story. For example, you are planning to add creatures into your story, then I think you should then label them with their characteristics, aspects, nature, abilities, and most importantly, their names. Or if you would be planning to make different types of magic elements and spells, then label them too! However, while you are planning all the details and plot of the story, you have to make sure that readers would be able to understand them. Make sure to add a few adjustments for the readers, and there! I think your fantasy story would shine all and then.
I hope I would be able to help with this, but as of now, I wish you the best of luck with your story! 