As it is now, this book is a standalone.However, given its ending, there is a big chance there will be a sequel. Regardless, you can read Jade Fire Gold as a standalone even if the book gets a sequel.
There is no spice in Jade Fire Gold. You see the two protagonists grow towards each other as they start having feelings towards the other. At the end of the book they kiss.
The epilogue of is short but it makes you crave more. As said before, the book is a stand-alone. However, in the epilogue, we get to see that apparently, Altan’s sister is very much alive, which could lead to a sequel. That said, there currently isn't any information that there will be a sequel to this story.