If someone asked me to map out the 'Caster Chronicles' reading order, I'd say the simplest route is to start with 'Beautiful Creatures', then jump into 'Beautiful Darkness', followed by 'Beautiful Chaos', and finish with 'Beautiful Redemption'. That's the core four. There's also a prequel novella, 'Dream Dark', which slots in between 'Beautiful Creatures' and 'Beautiful Darkness'. I read it after finishing the first book, and honestly, it adds some nice texture to the world, especially regarding Ridley and Link, but it's not strictly mandatory to follow the main plot.
Now, there's a sort-of fifth book, 'Dangerous Creatures', which kicks off a spin-off series focusing on Ridley and Link. It happens after the events of 'Beautiful Redemption'. I approached it much later, almost as a separate thing, and that worked fine. It feels like a different energy—more road trip, less Gatlin Southern Gothic—so treating it as a new series start rather than a direct sequel makes sense to me. The reading order can get a bit muddy with all the extra stories, but sticking to the core quartet in publication order is the most straightforward path into Ethan and Lena's story.
A lot of online lists will include every single novella and short story, but unless you're a completionist, the main novels give you the complete arc. The magic system and the whole Castor vs. Mortal conflict get fully resolved by the end of 'Beautiful Redemption'. Everything after that is expanding the universe.